The SteamOS version is cheaper than the Windows version.Valve has already ported Steam OS to both the Lenovo Legion Go and the ASUS ROG Ally. Additionally the new Lenovo Legion Go S ships with Steam OS instead of Windows.
I guess it is good MS has realized that folks want the compatibility of Windows, but the performance of SteamOS and are looking to make a version of Windows for handhelds. Curious if they are going to allow it to run on "normal" desktops.