Looking at the case of Idtech5 used for Rage, Carmack explained that they wanted to make an engine to be equal amongst all gaming devices. I.E. PS3, X360. PC and Mac.
At first Carmack said the PS3 always became the limiting factor because of the assymetry of the Cell processor and less ram to work with. At the end of the day Rage requires 2 dvds worth of space, meaning the PS3 has an advantage with Blu-Ray because the textures do not require as much compression.
Exclusives have the benefit of making the most of the advantages of the specific console.
Killzone 2 has incredible graphics, and that's most likely associated with the amount of time the developers took to optimize the code for the Cell.
X360 is capable, but I think suffers from engines with PCs in mind.
What does VGChartz think?
How large is the benefit from optimizing code for one platform compared to optimizing for multiplatforms?
