Because there is another version of Dissidia: Final Fantasy coming out in Japan. Square Enix opened a teaser site for Dissidia Final Fantasy: Universal Tuning scheduled to come out on November 1.
No other details, not even the system has been announced. Seems like it could be the North American version of Dissidia: Final Fantasy — that is Dissidia: Final Fantasy with English voice acting, the arcade mode, plus a few extras for Japan. Square Enix has a habit of releasing international editions, but usually not this close to a game’s Western debut.
Update: As expected Dissidia Final Fantasy: Universal Tuning is an “international” version of Dissidia: Final Fantasy . The revised game includes the arcade mode Square Enix added for the Western release, over 100 extra character tuning options, and English voice acting with Japanese subtitles.
Dissidia Final Fantasy: Universal Tuning will be released as a retail game and a downloadble title on the PlayStation Store. Previous save data (i.e. save data from the Japanese verison) can be transferred to Universal Tuning .