User blog comment:Saratje/PC release date explained - Skyrim: Dragonborn DLC/@comment-62.178.253.65-20121202130204/@comment-66.87.4.87-20121203104436

But Valve is making money from it, not Microsoft. Bethesda isn't licensing to Miscrosft because You aren't using Windows to play it, you're using Steam, which uses Windows to run. Steam is third party software, so it's not  like Microsoft has any reason to make agreements with Bethesda for PC, when Valve gets all the customers. Just like Valve doesn't give Microsoft any money for Half-Life or L4D because Steam uses Windows.