I feel like we're past the point were processing power is holding video games back from a design point of view , i can remember when wrestling games couldn't handle more than 4 characters playable at once, or fighting game sprites being scaled back compared to the arcades with fewer animation frames , or racing games being limited to so many cars on the track.
crysis 3 on pc vs crysis 3 on xbox 360 , the visuals are amazing on pc , but its still the same game.
when it comes to consoles its not all about cost to performance either , the biggest draw back with computers is the interface , the pc for proper gaming requires you to run windows , which is way more powerful than you need for a system that sits under your tv in the living room, then you have the problem with some games requiring a keyboard and mouse as there inputs.