There are good reasons for that:
1. First of all its easier not having to think about the requirements, I don't want to have to keep checking my specs to see if my rig can handle 'teh powerz'! And then you have the likes of Crysis popping out and making my rig cry. Yeah, the sequel may have suffered from severe graphics satuaration to work on the PS3 and 360, but its more accessible and you'll find more people playing online than the PC verison.
2. Controllers, while you may be able to play with controllers on the PC versions, the console versions just feel more natural, vibration, keyed in controls so you rarely have to change or tweek anything.
3. I'd rather use my PC space for more relevant things to be frank, gaming takes up too much ram and too much harddrive space and the constant need to upgrade or get more space to play sims 3 3/9 gbs, Crysis another 3/9 gb and god knows what else, just becomes tedious. My systems play games, my PC is used for everything else.
4. Network, playing multiplayer is fun on the PSN and XBL, maybe not in the same league as some PC games, but nevertheless, fun regardless.
5. PC games are moving over to PS3 and 360, some exclusivly and others multiplat, no matter how you look at it, other than graphics, there isn't really a compelling reason to pick PC gaming over console gaming, not to mention the console exclusive games as well.
6. Games may be cheaper on the PC, but that's easier to handle than spending on a decent gaming rig to play less games. I personally only buy AAA games and specific ones I'd like, so the costs aren't that much, and even still, many of the games I want and buy are often exclusive to that console, so whether they are more expensive makes little or no difference as they can't be obtained anywhere else cheaper.
Conclusion, PC gaming is awesome, and if you can't find a good reason to own a console, stick with the PC for mod options, cheaper pricing and easier controls in certain games. But if you prefer to use your PC for graphics, music, movies, programming, writing etc and more serious things and care about harddrive space and all those other nitty gritty things, a console just makes life easier.