MGS4 is the game which really makes me think FFXIII can break 1 million first week in Japan with utter ease. That one hit 450k first week in Japan and does not have nearly as much of the worldwide appeal which a FF game has. Install base does not matter much but easily another million PS3 sales in Japan should happen within a year with games like SF4, RE5 and Yazuza 3 releasing.
I dont usually care for game sales but FFXIII, Versus and GT5 are 3 games which I hope do very well, so much time and effort go into those games. I will buy those 3 so devs get my money, everything else nothing but a rental. :D