Linux's support is defined by commercial use by businesses, not home users. Hardware and software makers do not get their money from home users, they get majority of their revenues from businesses.
Name me a piece of software and I will name you it's OSS replacement (Which is often superior)
Businesses don't use open-source, open-source is not trusted and is unreliable. And unreliability comes from the fact that the software is free, it does not bring food to the table and the programmer is free to quit programming it anytime. There is no true guarantee of technical support.
I don't know if there is any comparable open-source software to AutoCAD for example. But guess twice if businesses will buy AutoCAD or download open-source alternative. They will go with AutoCAD.
yes, don't forget WINE - most of your "ZOMG! gotta have this application! it doesn't run on linux!" things run in wine, including many games
"Maybe it works, maybe not" is not what businesses want to hear. Any emulator is unreliable.
PS: making your ATI card work on linux is laughably trivial. I have less problems getting my card working on Fedora Core 5 than I do on windows
I have an ATI card. After installing FC5, installation went fine and post-installation configuration as well. However, where login screen was supposed to be, there was black screen instead. (K)Ubuntu graphical installer presents a black screen as well, I can get Ubuntu installed if I use text mode installer. After installation there is again black screen where login is supposed to be. I can install fglrx drivers when I boot Ubuntu into recovery mode, after that it works. Later I decided to give FC5 a new chance, this time around FC5 installer wouldn't even start, not even text mode installer. Re-burning the image did no good.
Every distro that has a graphical installer reeks of poor quality. Of the most popular distros only SuSE worked out-of-the-box without black screens and driver installations, sadly hardware video acceleration did not work and graphics were slow. Majority of the other distros will give a black screen either already during installation or when you're supposed to login for the first time. FC was the worst, the installer did not even start up the second time.
The bottom line is that open-source community is unreliable, businesses do not trust in anything that has not been made by another commercial business. I think it is called capitalism.
Edit: Business critical servers always run either Red Hat Enterprise Linux (RHEL) or Windows Server. RHEL is backed by Red Hat as a company, Red Hat supports their product.