When you purchase a new Windows PC it often comes preloaded with a 30 day demo of software a, b and c and a lite version of software x, y and z. The vendors of those programs pay large volume manufacturers to preinstall them on new PCs and cummulatively those payments add up to more than the cost of an OEM Windows license.

Although it irritates me that PCs invariably come with Windows preinstalled the 'Windows Tax' to the end user is actually probably zero.

If you're determined to get an OS free PC in the UK ebuyer's Zoostorm range are the best I know of. For laptops they only seem to have pink in available at the moment but I think it looks a decent spec for the money.