I don't know if it's just a lack of demand, or if it's a matter of trying to
support Linux for people who buy Dell PC's.  The real question would be
whether you can buy a Dell PC without an OS installed now (and whether the
price is lower than the same PC with Windows).

I think the kind of people who want Linux on their desktop buy from local
custom builders or build their own.

I have heard that the market for pre-loaded Linux laptops is measurable -
something where the average Linux guy wants the hardware issues resolved
before it arrives.

Then again, I think supporting Linux for end-users who don't know where the
"any" key is, think the mouse is a foot pedal, and are trying to fax by
holding a document up to the screen and pressing "Send" is mind-boggling.