You don't know that yet.
@Phreak: That was back when the game was first shown, and they said the 360 version was slightly ahead of the PS3 version. In recent articles they were saying that they were having trouble streaming data on the 360 and keeping data size down.
Still, the only way I can see this being true is if they found some way to fix the framerate issues they were having. If it were coming out this month, they would have like a week to work on it before it would have to go gold.