Well in the other thread with the Interview w/the director and producer they said they wanted to release it overseas (NA) and the 360 does have the biggest userbase in NA for HD consoles (still overall in NA too), so the game does make sense being on the 360.
Plus MS probably helped a lot with the production costs (in exchange for the timed exclusivity), so Namco has even reduced the amount of $$ they need to make to profit on the game. Namco already has a really good relationship with MS (e.g. Eternal Sonata, Ace Combat 6, Beautiful Katamari, etc), so this just further reinforces that strong relationship they have.
starcraft: "I and every PS3 fanboy alive are waiting for Versus more than FFXIII.
Me since the games were revealed, the fanboys since E3." 
Skeeuk: "playstation 3 is the ultimate in gaming acceleration"
