@ Munkeh
PC games may offer even higher resolutions but I think we will be getting to a point where higher resolutions (beyond 1080p, you will need a very very big display and sit very close to it to notice any difference, not recommended for your eyes) and maybe more effects won't matter so much as compared to enhanced physics, AI, huge environments and game complexity. At least with regard to realistic games I think overdoing it with effects may actually result in a less realistic game. The fully destructable environment talked about with regard to Killzone sounds really promising, no longer while firing a rocket at a tree it will be left standing as if nothing has hit the tree, a tank won't be stopped by fences or walls. Folding@ Home is a good example where the PS3's Cell processor is able to outperform massive calculations done by the PC CPUs 20-30-fold.
The PC gaming market has shrunk roughly 40% these last 5 years, so there's less reason for game companies to justify dedicating their resources on getting the most out of PC graphic cards. I can't speak for others but personally I am done with constantly upgrading my PC for playing the latest and greatest games.
Hopefully Epic's UT3 will be very impressive on the PS3, afterall Epic is trying to sell their game engine to other developers. Although Resistance is excellent to play with a game pad, IMO it's a positive sign UT3 for the PS3 will support keyboard and mouse, as like I said I am not intending to upgrade my PC yet again before it breaks down. 
