Most computer enthusiasts install xp pro on some nice hardware, get a spiffy background for their desktop, run as administrator 24/7, play games, and surf the internet. A lot of computer enthusiasts install xp pro back in the day, and they use it just like home edition. So what ended up happening is many of these computer enthusiasts spent twice the money on an OS for the features they aren't going to use, but in fact don't even know that they only own xp pro for the cool factor of "it's xp pro bro!".
I think this way about a lot of things...which is the most cost effective and best route for a person to make a purchase based on what they will never be doing and what they will be doing with something. This is the thought process i use when helping anyone buy or suggest anything for computers based on a users needs and wants. Many times i end up telling people not to upgrade or buy anything because what they have currently suits there needs fine (and even sometimes what some people are trying to achieve is just unrealistic).
If someone has a p3 with 512mb ram and xp, i'm not going to tell them to upgrade if all they do is surf the net, write up documents, listen to music, burn cd's, play solitaire, and watch the occasional dvd movie. A p4, or something dual core isn't going to help this person's situation at all and would be pointless. I would however help them get a new hard drive since p3 systems are sort of old.
Anyway, you have two reasons for xp pro. The biggie was that it was free, the second was that you'll actually sort of use it. So that's cool.