According to Siliconera, Final Fantasy XIII's 360 port has not been announced for release in Asia. The team is currently focused on finishing the Japanese PS3 version of Final Fantasy XIII. "The priority is to bring it to the PS3 first." Once the game releases in Japan, the team can then work on localization and porting it to the Xbox 360. This may mean we're going to suffer through an intolerable wait for an English-language release.
The main reason behind today's announcement is obvious: the Xbox 360's significant userbase in countries not named "Japan." However, although Final Fantasy XIII has been announced for Microsoft's console, Versus XIII is still in development as a PS3 exclusive. Of course, considering today's revelation -- will that exclusivity truly last?