The Left Coast environmental law (California, Hawaii, Oregon, Vermont? and Washington) requires that high powered computers have the most efficient components and many computer makers aren't including such components (i.e. 80 Plus Gold high efficiency power supplies) in their computers to keep the costs down. If you buy a large computer with lots of expansion slots, you can get pretty much anything you want. If your seeking a computer that is compact in size and expansion capability, you'll likely run into trouble.
This video from JayzTwoCents explains what is going on: