While I agree that it is stupid to use a 360 game pad EXCLUSIVELY, It must be said that after using the PS2, game cube, X box, and 360 controller on my PC, I Prefer my 360 controller second to the game cube wavebird. The only reason i prefer it is that I had one anyway I find it slightly gay that I need some Microsoft USB fob, when I have a box to use a GC/PS2/Xbox controller.
What I will say I like about my 360 controller is that its a perfect solution to school cafeteria gaming. The other day I was playing UT2K4 making my friends pelvis dance down a hallway via flack cannon, in public. and all I had to do is have my 360 controller in my laptop bag, which I already have a pocket the perfect size for in my bag. I still say the best controls for an FPS are mouse and joystick. But since a joystick doesn't fit well in a backpack being shared with a laptop as well as 2 hundred pounds of books. I'm going to say the 360 is a better solution. Especially if like me you have Mugen on your machine and find old 2d fighters stupidly fun.
Ok I'm a long way off topic. back to the "why"
I'm going to guess its not because 2k is a bunch of evil minded dickheads. I doubt their in their secret underground lair going "MUAH HAHAHAAAA! Now those fools we call our consumers will need to buy a controller that we approve of!" My guess is it's one of two things;
They where given a offer from Microsoft that was to the effect of "We have FAR too much money, would you like to restrict your game pad setting for a few yachts?" and 2ks response was probably "Hmmm, ok"
OR
2K believes that is the wisest choice for the market.
If your DESPERATE for an alternative Google up "JoyToKey" its an oddly powerful program, ive used it for Autocad, and photoshop in the past.