The lights are on
Quite a few reasons.
PCs, as a platform, have more power and capabilities. Such as, browsers, software, programs, etc.
Games are usually cheaper, starting off at $50 or even $40 for new releases.
Digital release platforms like Steam, Impulse, Direct 2 Drive, and a few others.
Mods. Games like Oblivion and Neverwinter Nights have thriving communities that constantly bring in more and more content for the game or change it around entirely.
Emulators. Want to play an old DS or SNES game? Just go grab an emulator and the game, and voila.
Free online. Though the PS3 does have a free online service (as I understand it), on the PC no one is stopping you from hooking up onto Steam and playing multiplayer.
While this is a thing of the past, general patches were a PC exclusive, but now consoles do get patches regularly.
There may be a few others, but I don't remember them now. The update cycles for PC hardware is a bit shorter than the console cycle, but you're only putting in more RAM or a video card, so its not that much more expensive.