In a free market
the OEMs wouldn't fear putting another OS on a machine.
MS wrists have been slapped quite a few times now, and the GUI is ready for numpty consumption, they will have an easier time on a Linux desktop rather than a Vista one, so makes sense.
Has SUSE or RedHat actually been preinstalled by anyone, ASUS used their own bastardised Xandros variant for the EEE. Hmm Dell seem to have gone RedHat and Ubuntu.