Metal Gear Solid and Final Fantasy games have (typically) been a well known franchise games which is one of the best games of the generation, and are released (practically) exclusively on the most popular system that was affordable and had already sold very well.
The PS3 will not be particuarly affordable, will have not sold (particularly) well and will not be the most popular system when these games are released; these games are going to sell at a far lower level than their PS2 counterparts sold, just like every other PS3 game that has been released.
Killzone was a mediocre title released for the PS2 that didn't sell well. Killzone 2 is being sold heavily like Lair was with a focus on pretty screenshots and videos with little/no attention to how the game plays. I see very little reason to believe that Killzone 2 will be dramatically better (or sell dramatically) better than Killzone.
