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What about Halo 3 being found in Steam's registry? What about MS making games exclusive to Steam recently (like Age of Empires II HD)? I'm sure they care about the sales, because they could get quite a few on Steam. On Xbox Live (windows 8)...not so much. Did Halo 2 help at all? It got slammed for having Vista as a requirement by reviewers and by consumers so I really doubt they will repeat this mistake.

I don't think Gabe Newell has anything to fear at this point, because like I said, MS are still porting games to Steam.

Some of those points are rumors which may or may not materialize, much like this one.

Im just speaking what makes sense for Microsoft and their converging ecosystem strategy. It's all about ecosystems at this point and while standalone MS games are still sold on Steam, those days are slowly coming to an end. It won't happen tomorrow in even in 2-3 years but as Win8 adoption grows, they will move away from supporting any game store other than their own.

The real differentiator for the ecosystem battle is to release titles which span multiple platforms and devices and Microsoft can't do cross platform support on Steam, like they did for the 2 xbox live titles listed above. 

Having  a vast SW open market, that doesn't rule out the possibility of using closed markets too (and NEVER being forced to use just one of them) is, together with HW open market, leaving almost total freedom and keeping SW prices down, and HW too unless you want high-end components, the biggest reason of PC success. Trying to close PC's SW market would simply leave a vast potential market to Windows competitors.

I don't think Microsoft is making PC a closed platform by focusing their software releases through their own store.  It just makes sense to go Windows store route for everything in a couple of years but I don't see that being the only option.

My company has developed a video streaming app for Win8, and WinRT. It would take 2 daysof work to port it to Windows Phone and Microsoft has approached us to make it for Xbox using a brand new SDK... The software tools for all these platforms are very similar, the QA process is the same, advertising API's are the same. The whole idea of convergence isn't about locking down, but convenience... 

Having  a vast SW open market, that doesn't rule out the possibility of using closed markets too (and NEVER being forced to use just one of them) is, together with HW open market, leaving almost total freedom and keeping SW prices down, and HW too unless you want high-end components, the biggest reason of PC success. Trying to close PC's SW market would simply leave a vast potential market to Windows competitors.