So the Xbox 360 versions run faster & smoother. There seems to be a lot of discussion about performance issues of the Playstation 3 on several websites. One of the employees of Sony tackled the subject on Sony's PlayStation blog:

"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."

EA has been developing on Xbox 360 hardware a full year longer than on the PS3, so this could explain why it's difficult for them, but 2K is having the same issues with All-Pro Football 2K8, a game built from scratch to be released on both platforms.

Playstation Blog