Im gonna buy the game to PS3 and PC because both of them are stronger than the Xbox 360.
Not to flame you or anything, but you are totally wrong there. The 360 is much stronger then the PS3 when it comes to multiplatform-games, every single release (except FF) has had better FPS, graphics and such on 360 then 360, and often by quite a bit. The 360 is easy to code for, just port the PC-version and change controls, while the PS3 i2 "special" and needs "special treatment" while coding, making it hard and expensive. Btw, the 360 got more GPU (graphics power) and Ps3 got Cpu, we all know what matters when it comes to gaming
If you are going to play on Ps3 with 3D enabled, you should really expect quite a de-grade when it comes to graphics. The hardware is really limited and to support 3D the graphics and fps goes out the window in every game (this gen-consoles are to old).
I would suggest you get decent PC for 3D gaming, that way you can keep decent grapchis and avoid framedrop while playing
OnT:
Not really, all platforms deserves a chance to test the game.
That said, Killzone 3 for PS3 will have better graphics and such, hence a demo would only hurt sales.
For PS, well there are always ways to find out... (review, gameplay videos, system requirements) and playing Crysis 1. That said, a demo for Pc would probably not be a bad thing.
Really, 360 needs a demo too. What we got now is a beta in the words fullest meaning, full with lag etc. If the final game is anything like it I won't get it since it is Cod mixed with Halo + lag at the moment. But I'll wait and see what the future holds