Shinji Mikami has commented his studio's decision to develop Vanquish for PS3 first was because he wanted to make sure it was not a shoddy port. Mikami said once his team has nailed PS3 development, it'll move onto Xbox 360 development:
“The team knows less about making games for PS3 than Xbox 360, so we thought the sensible thing to do was to make the game on PS3 first then move it over to Xbox."We also found out that Mikami is opening up his new studio.
“If we can get Vanquish to a certain standard on PS3, we can make Xbox the same.”