Yes. Or at least their stick to beat Microsoft with when it come to negotiating access to the Windows Metro UI in Windows 9.
The desktop environment isn't going away in Windows 8, so platforms like Steam will still be able to run. Windows 9 though? Anyone who doesn't have a head full of rocks can see that Microsoft might decide that only "enterprise" installations of Windows get to keep the desktop UI.
Valve really, really need to be negotiating from a position of strength when and if Microsoft decide that's the road they want to take.
In order to be a decent bargaining chip they would need to bring more users to Linux desktop though. They can't really say "Give us what we want or we'll move to a platform with 1% of the userbase" without having their bluff called.
