Obviously a high end PC is going to look and play better than a console running the same game (or modded version of it), but what i like about the console is that you know that you can buy the game, and play it when you get it home instantly, without faffing around, and as the console ages, the game is going to continue to play the same way. Plus for online games, you know that everyone is on the same playing field, with the same equipment (i don't really care so much about this, but it's an arguement i've heard).
If i had a £1500 gaming pc, i would sure as hell play games on it (they are often cheaper than console games), but i do not, so it's a console for me!
EDIT: I actually bought an Xbox because i couldn't play the game i bought on my laptop. I got Just Cause 2 off steam after playing the demo and loving it so much i bought the whole game. But after faffing for around 2 weeks trying to get it to a playable level on my laptop, i relented and went out and bought an Xbox and JC2 to play on it. Best £250 i ever spent.