Often times, due to Microsoft co-marketing funds, "desktop real-estate" (trial-ware installs), and some other things - that end up offsetting the OEM's costs -

Often times, due to Microsoft co-marketing funds, "desktop real-estate" (trial-ware installs), and some other things - that end up offsetting the OEM's costs - you're actually paying less for a system with Windows installed then you are for a system without an OS installed. So the cost issue is mostly a non-issue, as to maintain the same profit margins the OEM will sell the non-OS system at a higher price. This is especially true for "basic" systems, were they sell them at almost cost price... As OEMs make all their profits on upgrades and higher spec systems that they can sell at a markup.