I'm not sure about the do so much more part - I mean, sure, they have better graphical capabilities at the moment, but the PS3 and XBox 360 are capable of so much more than what they do now so at the moment, one could argue that they are more powerful than PCs. It's more about how it is being utilized.
Also, while PCs have some serious graphical power, the game market is far more limited for PCs than consoles - you have your handful collection of western RPGs, your typical FPS/tactical FPS game, and your RTS, and that's about it for the most part, while consoles offer so much more variety such as rhythm games (i.e. DDR & Guitar Hero), adventure games (i.e. Zelda), fighting games (i.e. Street Fighter, Super Smash Bros.), eastern RPGs (i.e. Final Fantasy, Tales), strategy RPGs (i.e. Fire Emblem, the godfather of the series), and other quirky variety such as the Wario Ware games. Also, the control mechanism for console games is more natural & intuitive than PC games in general, the most notable exception being the RTS genre, despite its roots on console games (Herzog Zwei).
The large problem is that the PC gaming base is generally limited to those who think of themselves as hardcore. Few companies have attempted to expand this market, and many of those attempts end in failure, excepting a few notables such as EA's The Sims. This market is growing increasingly limited while many developers are able to expand on consoles due to the encouragement of making your product stand out with the deluge of clones and done-thats. This is probably why the PC gaming market has been dying in terms of sales.