Shortly after the Playstation3 was first announced, there were gripes from developers saying that the console was difficult to develop games for, especially where porting was involved. Well, the official word from Sony is that it is indeed more difficult to develop for, but only because there is more power to tap into.
It seems reasonable, but at this point in time there hasn’t been any real evidence that a PS3 game is much better because of the Cell processor. Sure, it’s powerful and rids certain boundaries that developers run in to, but is it all worth it for a console that’s more difficult to develop for? Aside from all of that, both consoles have some great games regardless of the hardware they are running on.
If your game starts on Xbox 360 you will have to re-engineer aspects of the game to run properly on PS3. This means additional effort. Some developers have been complaining about this but I don’t believe we can solve that. Xbox 360 is a different machine with good, but lower powered hardware in a different architecture. Developers have to view them as two different machines not as a common platform.
Source: Playstation Blog