A prefabb'd computer with the horsepower we like to have, is going to cost a considerable amount more, than if you buy the parts and do it yourself.. To me this is pretty elementary, in a lot of different aspects..
I think the key reason people like to buy a prefabbed PC is they like the security of knowing it will power on and work the way they would like, and if it doesn't, then they can lean on a warranty, or coverage on their purchase... The cost these days, to me at least, is closer in range than it used to be. Parts to build it yourself were pretty pricey compared to what you would pay for a Packard Bell or Compaq, but then again who remembers when the 133Mhz machines with 16MB or RAM cost $2200?
I know you old timers can do better than that too heh heh
-J