Can I use only a xbox360.

I'm not sure I understand...are you a game developer trying to make games for the 360? Cause they put out an SDK for the 360 if I heard correctly.
But if you're saying everyone in the world should stop making any games for the computer...well, fat chance. It's like having a mac person go up to Windows developers and say "Excuse me, can you just make programs for OS X now? That'd be great."

Ah. That would make more sense.
Consoles are not exactly the same as PCs, so it takes some time to work out exactly how it translates. You do know of course, that Half-Life 2 took a very long time to redevelop for the Xbox? To most manufacturers it's not worth it, especially when they don't see console players able to enjoy it.
There's also controls. FPS's and RTS's pretty much fail on consoles because you don't have a mouse. (you can tell...I'm no Halo fanboy) The differences go on.
But you'll never have all the consoles to play all the games, so just be glad you have a 360 and a lot of people don't.