As for the centralised leadership not making demands, what the **** do you think Bin Laden is doing on those tapes he periodically releases? Dictating his shopping list? Reading out the text of Harry Potter in Arabic? Ordering pizza? 
If you look closely at the writing of Family Guy, you'll find the jokes never derive from the plot. And I think that's totally gay.Alright, seriously now.
Mustang, I think you're a little confused on exactly what al-Qaeda is. So let's backtrack to the 1980s. The Soviet Union has invaded Afghanistan, and the only real resistance is a group of Islamic militants known as the mujahideen. When news of this resistance reaches the United States and the Arab world, the CIA begins to work together with thousands of Arab/Persian/Afghan/Pakistani Muslims who join the mujahideen, providing training, weapons, and even immunity from drug trafficking charges, so long as they continue to fight ther Soviet Union.
One of these Islamic militants is a son of a rich Saudi construction magnate, who co-establishes a militant organization that helps funnel militants, arms, and funds into Pakistan and Afghanistan to fight the Afghan Marxists and the USSR. He ends up splitting with this organization and establishing his own group...this is how Osama bin Laden founded al-Qaeda.
Now, it's 1990. Iraq invades Kuwait, and puts one of the world's largest armed forces dangerously close to the Saudi border. Osama meets with the Saudi Royal Family and offers to bring the mujahideen from Afghanistan to defend Saudi Arabia from the Iraqi army. However, his offer is turned down in favor of the US-led coalition. As Western armies start arriving in Saudi Arabia, Osama becomes more and more critical of the Saudi Royal Family for allowing non-Muslims in the land of the two mosques, and is eventually banished from the country, his citizenship revoked, and his passport taken away.
He flees to Sudan, and then manages to get a chartered flight to Afghanistan where he begins to really organize his attacks. At about this time, we have hotel bombings in Riyadh, attacks against American military housing complexes in Saudi Arabia, a failed assassination attempt on Hosni Mubarak, the first WTC attack, and eventually the embassy bombings. Osama is continually making demands and verbally assaulting the Saudi Royal Family for what he sees as a desecration of Mecca and Medina. al-Qaeda becomes a militant organization dedicated to the overthrow of Western-leaning regimes in the Middle East and North Africa, with its central leadership organized in Afghanistan and Pakistan. Many other organizations with similar ideologies pop up across the Middle East and become affiliated with the group--al-Qaeda in Iraq, al-Qaeda in the Arabian Peninsula, al-Qaeda in Egypt, etc.
So then 9/11 happens. YMMV on how it was allowed to happen, but it ends up being the largest-scale al-Qaeda attack ever. Members of the Administration begin to rally millions of grief-stricken, terrified, and vengeance-driven Americans for an invasion of Afghanistan. In this build-up to war, Americans allow the Congress to pass several pieces of legislation--the Authorization for Use of Military Force against Terrorists, and the USA PATRIOT Act. Because of their fear and perceived vulnerability, they resign to the Administration's assertions that the Patriot Act will keep them safe at home, and that the AUMF will completely destroy al-Qaeda overseas and bring Osama to justice. Anti-terrorism operations begin around the world, with Operation Enduring Freedom in Afghanistan and the Horn of Africa, both known al-Qaeda strongholds, and FBI/NSA investigations in the US.
In Afghanistan, NATO closes in on the Tora Bora mountain complex where Osama and his top lieutenants are believed to be hiding. The attack is so badly botched that it becomes widely-believed that Osama escaped into neighboring Pakistan, and what should have been a quick military operation to destroy al-Qaeda and capture its central leadership turns into a ten year counterinsurgency effort against an increasingly-better organized and supplied Islamic militant movement remnant of the US and Pakistan-supported mujahideen from the 1980s. In an effort to locate Islamic militants throughout the country, NATO begins offering rewards to Afghans to turn over suspected militants. Many militants, Afghans, and Pakistanis are arrested and detained at NATO military bases in-country.
Back in the United States, a loophole created by the Patriot Act allows the NSA to bypass the Foreign Intelligence Surveillance courts and perform warrantless wiretaps on domestic communications. Americans of Muslim and Arab heritage become inappropriately singled-out by the FBI and the NSA as "terrorist sleeper agents" and arrests are made.
The Administration becomes increasingly aware of a perceived risk in holding suspected militants in either Afghan prisons/NATO facilities or US prisons, and so the Detention Center at Guantanamo Bay is opened to house these militants. Because militants are not a part of any national army, wear no uniforms, and are a legal grey area in the Geneva and Hague Conventions, they are transported to Guantanamo Bay and held indefinitely in the prison camps, many as young as thirteen or fourteen. In an effort to gather intelligence from these suspected militants or sympathizers, the CIA and military bring in more brutal techniques to extract information. SERE specialists, who train US servicemembers to resist torture and interrogation, are brought in to use their training offensively against detainees. CIA and military interrogators become frustrated at the lack of information being extracted, and resort to brutal tactics, including waterboarding, to get
any information out of the detainees.
Because of the lack of credible intelligence coming from Guantanamo, the CIA and the FBI become increasingly convinced that many of the detainees are, in fact, innocent or hold no ties to organized terror groups. This becomes a problem in the build-up to the invasion of Iraq, where already-flimsy intelligence is being used to convince the United Nations and the Congress to gain backing for military action against Saddam Hussein. Members of the Administration are aware of the reports, but order the innocent detainees held longer so as not to give a perception of incredulity to the US war effort and counterterrorism intelligence program.
After several years in Iraq, a key leader of al-Qaeda is captured--Khalid Sheikh Mohammed. The interrogators at Guantanamo think they have struck gold--a major player in the terrorist network in their hands. Interrogations agaisnt KSM are some of the most brutal in the history of the Detention Center--KSM is waterboarded over a hundred and eighty times. Because of the high-profile nature of his capture and detention, details of the interrogations at Guantanamo Bay become better-known and better-publicized in the US press. The KSM interrogations allow Americans to take a better look at what's happening down in the Detention Center...and sources inside the administration begin to leak information that some detainees are in fact innocent, and that members of the Administration were aware. The Patriot Act, which was once viewed as a protection against al-Qaeda and other foreign terrorist organizations, now becomes more terrifying to many Americans than Osama bin Laden, and Operation Enduring Freedom begins to lose support.
After the 2008 election, Barack Obama orders the closure of the Detention Center, to great relief. However, as the Patriot Act remains in effect and OEF is escalated, the Detention Center remains open, alive and well. Americans begin to have misgivings over the intention of the new President to finally close the Detention Center, and with this final decision, their doubts and fears are realized.
Meanwhile, al-Qaeda is still operational, its central leadership unrelenting in its demands for Islamic Revolution across the Middle East and North Africa and the expulsion of the West from their world.
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EPIC TL;DR: al-Qaeda was formed with US-backing in Afghanistan, and has been always about overthrowing Western-leaning governments in favor of Islamic states. The botched intelligence-gathering efforts by the US have made the country less secure, and have done more to terrorize the American people than al-Qaeda could have ever done.
Credits go to BP for the briefing music I had playing in the background while I wrote it, that helped make it seem more doomsday than it probably should have.
