Really, I'd be looking at PC exclusives as any games that are multiplatform I'll most likely buy for my 360.
Do you mind me asking why?
Just that some multi platform games would be better on the PC, B:AA and RE5 being recent examples. Just plug in your 360 pad and enjoy playing cheaper games at a higher res with double the frame rate.
The two I mentioned are Live enabled as well so you should be able to log in with your XBox live account and get the gamer points and achievements.
Only downside, apart from some ports are naff tbh, would be no cross platform online. So if you have a big friends list on Xbox you wouldn't for example be able to play RE5 co-op PC + XBox.
I wouldn't recommend always buying the PC version mind, as some ports really are poor but it'd be worth reading up on the PC versions as they can be better.