After Microsoft surprised the world at E3 by announcing Final Fantasy XIII for Xbox 360, speculation quickly mounted about the Japanese version as the company was careful to specify its release.
At the time, it was quietly mentioned by Square Enix that the PS3 version would not be affected because the game was being developed for the platform for Japan first, and then it would be ported to Xbox 360 for other regions. Although this sounded clear enough, we now have further confirmation about the existance (or lack thereof) of a Japanese Xbox 360 version:
"There will absolutely not be an Xbox 360 version of Final Fantasy XIII for Japan," said game director Motomu Toriyama in Dengeki PlayStation magazine.
So that settles it. This will of course be a setback for the Xbox 360 in the region; it no doubt would have benefitted significantly from such a high profile title.
Update: Apologies for the misleading title!