Computer OEMs do not just put a lot of parts together and tally the cost, multiply by some magic number and so set a price. They pick price points, for example $499, that they think will hit a market segment favorably and then calculate their margins. If $499 is the price point, it is $499 with Windows or with Linux. Quite often different models are priced to make one or another individual model look attractive by the comparison. They may price a good deal at $499 and set a real bare bones model at $449 and an upscale at $699. The user sees that he gets a lot more for an extra $50 with the middle model and doesn't loose much by not going the next $200 and so the $499 looks like a sweet spot. These guys are not geeks or rubes. They sell tens of millions of units a year and have tens of billions of revenues.