PCs have bloated operating systems that have lots of intrusive "services" constantly running, each fighting for dominance of your precious processing power. On consoles that OS is built and optimized just for the games, and doesnt require all that much juice to run.
Think about it, the PS3 with 256+256MB of ram and GPU manages to run similar games running on PCs without a hitch. Yes, it lacks newer features like tesselation etc, but the graphics is far from ugly, but it requires less resources to run than a PC for example on the same quality. Imagine what twice or three times the PS3 spec will be able to achieve.
I do play more games on PC these days, but it wasnt a cheap setup (mentioned my monster laptop here before which is in the excess of 5k). A console is a couple of hundred dollars for graphics a PC with the same price just cannot offer, even today.