It all comes down to demand and volume.
HP used to sell some systems with Linux loaded, but the demand was very low.
Dell, HP(and Compaq), Gateway, Lenovo are all high volume operations
selling millions of consumer PCs. While the popularity of Linux is growing,
it is not yet at the level where most of the vendors are going to put Linux
on. (Although we saw the Slashdot article that Lenovo is preloading SLED10
on the T60P Thinkpad).
I think you will see more companies preloading enterprise Linux on some of
the higher end business desktops and laptops, but not on the consumer
systems yet (at least in the US).
--
Jerry Feldman