Now, I'm a great believer in letting people use whichever damn computer they want. And Windows XP is no where near as bad as Windows used to be.
But, for my line of work (scientific computing), if I had to use a Windows PC, I'd have to download and install lots of different software such as Cygwin, an X11 client, SSH client, C++ and FORTRAN compilers, etc. Whereas with my Mac it's all built into the OS and works flawlessy. Of course I could just use Linux but then I'd have to mess around getting the sound or wireless to work. I probably would never be able to get it to connect to an overhead printer.
So, I like Macs as they're like Linux that actually does work*. The University paid for it so the cost isn't really an argument.
* I know Ubuntu works almost as well now but I got my laptop 2.5 years ago when Ubuntu wasn't quite as good as it is now. Even after 2.5 years there's no reason to replace my Macbook.