there are innumerable reasons to buy an xbox:
--there are many good controllers for xbox (Logitech), not to mention a PS2 controller adaptor
--Xbox can be modded to:
--make it a media center PC (complete with internet browser & scripts to automatically stream sites like Youtube & give you weather updates, etc)
--it can rip & store games on the HD
--it can emulate any system up to PS1 & store & play all the games of all those systems (Genesis, SNES, NES, atari, sega master system etc)
--most of the games playable on both systems are better on xbox (including 2K5); eg better framerates, shorter loadtimes, clearer resolution, fewer jaggies, etc
--it costs ~50 bucks now if you look in the right places
a better question is why
wouldnt you get an xbox if you want to play 2K5?