The thing with OEMs is the sales they run. Take for example this HP.Any examples? Most of the computers on Dell's site look like rip-offs, even the ones that cost <$1000
Take the base config, with the (currently free) upgrade to 2GB of memory, and it's plenty for anyone who just needs internet/email and the other basic stuff. For $450. Not even a shipping charge (atm). Even if you could build a comperable system for that price -would be difficult, IMO- I doubt you'd save enough to make it worth it.