You make a good point, and its something I've been thinking about recently as well. And for people who ask me, that's what I tell them, that they're better off buying a Dell or something. But:

1- I freakin' love my case. The computer has been non-functional for about a year now, but I still have it sitting prominently in my office, obscuring the cheapo Dell that I got for $50 from an office. This is purely a personal, non-logical reason, but it's a reason.

2- The prices are not quite as competitive as you (or I) thought. Plus, you don't get quite what you might want. I just put together a fairly plain Dell Studio desktop together (without a monitor), and a comparable system would cost about $1020. That's pretty much exactly what I was planning on spending, and...

3- The Dell has a lot of things I don't need: an optical drive (that's not as good as mine), Vista (I have my own OS discs), and a standard 500GB hard drive (I have plenty of storage, I want a fast OS drive, and there's no option for the WD Raptor).

4- It's fun to put your own system together. Granted, there are some headaches, but I've always enjoyed it.