I think I read somewhere that Square Enix's order-to-do-things-with-FFXIII list is somewhat I like this:
1. Release PS3 version for Japan
2. Make 360 version
3. Release 360 version and PS3 version in the US and Europe
Supposedly Europe and America are getting it at the same time, but it's been a long while since I read it, and I doubt something like that ever happened. So it's doubtable.