Sure I hope Valve makes good money on the transition from Microsoft to Linux. Probably they are only the first in a long row of game producers.
Microsoft has pressured many of them very hard so they have to "bleed" money for simply using Windows as a platform. As Valves Steam has shown Linux is an even better platform so I think that makes the choice easier for others.
Microsoft has overestimated their position in the Computer market yet again:
They started out with the ambition that everybody who has a PC must pay to Microsoft. They claimed that Linux had Microsoft patented components so even those with Linux PC's should pay. MS failed to point out what that should be and has never been able to name even one single component. Instead they threatened to sue everybody who used Linux.They called it "cross licensing" and the only Linux distro that has paid up is Novels Suse.
MS made "an offer that you can't refuse" - Corleone style.
The only thing offered is the absence of a MS lawsuit. Valve did not accept this style and said goodbye to Microsoft.
That is deserving of a reward. But the main platform for gaming will probably not be the PC in the future - but the dedicated boxes like the
Steambox and those will run on Linux.