I concur with BMaker11 -- the PS3 exclusives are going to be the first apps to really showcase the PS3's potential, just like 360 exclusives showcase the 360. This has always been the case.
KZ2 looking awesome is not all PR spin. It actually is a great looking game, thanks to its exclusive nature. It utilizes some rendering performance techniques (deferred rendering, primarily) that are, for all practical purposes, unusable on the 360.
Crossplatform games aren't going to radically change their game pipeline to support deferred rendering on the PS3 and not on the 360 -- that would hike dev costs past what the developers deem worthwhile. Although, eventually, as 3rd party engines mature, its inevitable that the PS3 versions of crossplat games *will* use deferred rendering and make better use of the SPUs, and the PS3 will finally demonstrate what a great platform it is.
KZ2's main reason for existance, from Sony's perspective, is to demonstrate the power of such techniques. To raise the bar, and *force* 3rd parties to work harder on the PS3, or look bad in comparison. Thus, even if KZ2 doesn't succeed financially, it will succeed strategically, as long as it reviews very well.
Several of Sony's exclusive titles this year are "demostration"/"wow factor" products -- designed specifically to showcase the PS3 to the developers and media (and consumers). KZ2 (rendering), MAG (scale), Infamous (physics), etc... all are probably products that could never make the transition to the 360 without some serious toning down.
