And lo Microsoft saw the App Store, and knew that it was good…
Basically they fell in love with the idea of getting 30% of the app/game market for desktop windows, and announced that the Windows Store was the way to go.
Valve (perhaps somewhat ironically) saw this as monopolistic behavior that threatened their biggest cash cow, and thus saw a need to reduce their reliance on Windows as their main market.
I’m a bit out of the loop here. What happened with Microsoft that drove Valve to create SteamOS?