Let's face it, there are three things keeping Microsoft's OS in business: the Office ecosystem, games and people who spent their whole lives learning one way of doing thing, and don't want to change. Everything else not only can be done better by someone else, but is being done better by someone else.
With every new OS release, Microsoft themselves screw the people who fear change. Office is still the cash cow, but between LibreOffice and the Googlighting Stranger, their desktop suite is only a few years ahead. I can't comment on Sharepoint and Exchange, so I'll concede they probably play a major role in many businesses, and that many of those same businesses have no interest in Windows 8 Metro. Finally, there's games. Games, and DirectX games, was the reason to buy Windows. Hell, it's the reason I run it. But, in the heavily politicized corporate environment of Microsoft, games have a problem, and that problem is spelled XBOX. So we get abominations like MS GameZone, Games For Windows Live and Games for Windows Marketplace, or whatever they're calling it now. The Xbox people can't have windows cannibalize their games. This is how Microsoft lost to Linux in the HTPC battle: an Xbox belongs in the living room, not a Windows Box. Things have gotten so bad, the other players in the industry have their own
Microsoft-Free group to promote gaming.
So Valve brings on board a developer with demonstrated skills in making cross-platform gaming tools. If they were able to produce a set of tools that allowed games to be developed and easily ported between the various full flavors of Linux, Mac, PC and Android, worked on Chrome OS, and connected to the largest online game delivery platform in business, well, wouldn't that be cool?
Don't worry, they'll probably do something less ambitious and more profitable.