In addition, Final Fantasy XIII will release in Japan first -- and then will be localized for the international audience. That means Japanese gamers will enjoy FFXIII on PS3 long before the rest of the world will see it go multiplatform. Hashimoto says that the Xbox 360's large install base in English territories is what led to the decision to make the game multiplatform. Because the decision was recent, there's no way of estimating how many discs the Xbox 360 version will be.
Also, Final Fantasy Versus XIII is still in development as a PS3 exclusive.