Its diminishing returns - consoles are quite powerful to render nice graphics, but not powerful enough to render it properly, thats why You have awful IQ, awful lod streaming systems, awful textures etc.
And when You compare raw processing power than PS3 is like 10-12 faster than PS2.
On PC You have the same game [like BF 3] in almost twice higher resolution, in double the framerates [its already at least 4 times stronger than PS3], with more than twice as many players, with much bigger maps, better LOD, better textures, better particles, more effects etc. PC are already using more than 8 times power of current gen consoles efficiently. It is generation leap, it has to be, we are 7 years in current gen, it would be stupid to not to be there.