Afaik, Microsoft doesn't make much from large OEM sales since they give such a steep discount. I asked Lenovo to reduce the price on my laptop because I wouldn't be using Windows, so they gave me ~$40 discount and asked me to not enable Windows (which I didn't). This tells me that Windows for OEMs is around that price, which is less than half of the retail price.
Also, a $400 laptop is hardly comparable to a $1500 Apple laptop. I've had one of those, and the hardware really sucks, and stuff starts breaking within a year. It may have the same CPU, but the rest of the components are really crappy. If you want an closer comparison, compare high end laptops with the Apple laptops (Lenovo X- series, Dell XPS series, etc), which run at a much more similar price. If they're lower, it's because they have more competition than Apple does (Apple doesn't license its OS to competitors, so if you want their OS, you must buy their hardware).
