I have proof... the playable demo showed by SE six months before the 360 the new playable be showed was a lot better than the final game in graphic terms.
A SE excutive said itself that the cut content removed from the game due the multiplat was enougth to make a new FF game.
And I will not complain about the fact the PS3 had to be delayed one year after finished to wait the 360 port and to be fixed to have comparable quality with the other version.
But MS paid for that so I think that's fine after all..