Sure everyone would love to have a 928. But the reality of the matter is that most people wouldn't know what to do with all that power. The average home computer doesn't see much strenuous activity beyond deleting the internet temp files. For those people, the Escalade is a perfect option.
Then there is that niche of people that like to game but either don't know how, or don't have the time to tinker with a computer. For those people the hardcore OEMs mentioned earlier are more like a 928 but a tad neutered. These companies aren't large to the point of obscenely bad customer service and they provide a pretty decent product. Price is a bit of an issue, but look at it this way, you could pay a little more and get the full service provided with a new system purchase, or waste time fixing the computer yourself. These days, time is money - the opportunity cost of buying from an OEM is much less than that of building your own system. Besides, chances are if you can afford any of the L33t OEM computers your time is better spent doing your job and leaving the computer tinkering to someone else.
To put this in another set of car terms the run of the mill OEM like Compaq would land in the family sedan or minivan range. I'm going to use cars that are currently in our parking lot, let's say those slow poke OEMs are like a Subaru Forester. Not exactly the sportiest or dashing but it will get you places and it will get most jobs done. The hardcore OEMs would land in the category of an Acura Integra. We have lots of those in our company at the moment, that and Civics. Then the last, and most hardcore would be the home-built overclocked monster with the U2W setup and triple fan coolers with a peltier system snaking through the bowels of the system. In our little land this system would have to be the Integra Type R (no comment), or possibly one of the rice rockets that dwell amongst those known as IT. These cars will get you where you want to go, and FAST. But they are also delicate like the pear blossom. These things have to be pampered, driven over the slightest bumps at angles and all warranties are voided once those after-market parts hit the engine and exhaust systems.