Final Fantasy XIII needs to do well for Sony to have any further Square Enix support. That pretty much goes without saying, I think that is the reason Sony are rushing games like Gran Turismo 5 and co to release before FFXIII to increase the user base and help ensure sales.
What Sony really needs in Japan right now is a price drop. Expensive system + 1 good game, rest crap = Crap sales.
Sony have a lot of games coming out that Japan will buy, but they need to get the price sorted. The PS3's problem is that it is just too expensive.