@RobGreenly: You heard wrong. $80-100 is the price for Windows AND Office. http://www.tomshardware.com/news/Windows-RT-Windows-8-Licensing-Supply-Chain-OEM,16267.html
Regardless, Microsoft would be putting themselves in a precarious position legally if they undercut OEMs in the way you suggest... even if it made sense to do it, which I don't believe it does. Undercutting the OEMs would mean less profit for Microsoft. It's a complicated calculation, and Microsoft does have to be careful here, but I honestly don't see any way that them making hardware means there's no room for OEMs. There is the chance OEMs would opt for an alternative (like Android) that would offer them a larger profit margin, but that's just more reason why it's not a good idea for Microsoft to give the OS away for free to customers of their hardware.