This is a point that's been brought up time and time again, for as long as I can remember. There are two other points to remember, the vast majority of gamers don't need a $1,500 machine. For a computer capable of playing halo 2, you can go buy one for $300-$500 from a major dealer. No big deal, that's about the same as an XBox. Any more that you spend than that is above what consoles can do (DX10, etc). And I agree with you, more than that isn't needed. So, those that buy the $1,500 computers are generally die-hards/fanboys. Not always, because here comes the clincher... you can do other things on a computer besides play games, you know?
For me, my gaming pc is also my workstation. It's rigged out for heavy computation, so I'm getting a productive element of the family and a gaming platform for the same price as a console. Not only that, I can buy a controller if I really wanted one for $30, so even the controls of a console can be mimicked.
If you asked me, yeah, I did spend more than $500 on this computer, and it was very first-gen tech when I built it. However, I've built several extremely powerful computers in the last few weeks for, say, $800 dollars for multi-processor, windows, office, etc.
Lastly, how many consoles do you own? Each generation of consoles generally has about three, now. Nintendo, playstation, and xbox. Add the prices together to get a platform that can play anything and you're at more than a pc ;).