Microsoft needs to make a deal with Valve and offer money to developers implementing touch-screen support. Indies is a group Apple/Google are failing to address properly.
Microsoft essentially tried to destroy PC gaming with Xbox and completely neglected games on PCs. (Microsoft has publicly admitted the latter.)
Microsoft has been trying to lock down their eco-system with Windows Store which if successful, would be a death blow to Valve.
Microsoft has created a support nightmare with their OS for games in terms of games, from usability to driver reliability. Look up Gabens comments on Vista and Windows 8.
This is what is driving Valve to do SteamOS and Steam Machines.