I think it's a little disingenuous to compare Windows to SteamOS like this. Microsoft has quite a bit of pull with hardware manufacturers; there's a strong incentive for PC companies not to put out hardware that doesn't work with Windows (and I'd imagine extensive tests are done before releasing any such hardware to ensure that everything works with Windows, presumably with some degree of communication and cooperation with Microsoft). On the other hand, there's virtually no incentive for a PC maker to make sure that their hardware doesn't break things for SteamOS.