As this and last year have shown, there is no single game that will drive a console's sales above its normal average. Halo 3, GTA4, MGS4, GoW, etc., have all released and they've not been able to raise their respective consoles' sales far beyond normal levels.
More recently, case and point, MGS4. Yeah, it's sold 2 million in just three weeks. But it didn't cause the same kind of stir in the hardware sales. Yeah, hardware spiked a little. But eventually, it all normalized.
So people who think that just because FF13 is going multiplatform will mean the death of playstation are only being far too emotional. If trends with huge titles so far are to be followed, this news won't be much of an effect on hardware sales. And don't even say that FF13 is bigger than those other titles before. In fact, the ripple it will make would be much less too, since PS3 is still getting it.
I really don't see what the fuss is all about. In fact, we should be happy that more people will be able to play this amazing game. Stop being emo fellas.