You are absolutely correct in this one. The people at MS are not dumb, the "one and only stack" is no longer. Microsoft is therefore, in a rather pragmatic manner, moving to stay relevant. You can see this in their open-sourcing a lot of their stuff, not only the .Net stack but also their C# compiler (Roslyn) etc. For anyone who is not a paranoid, retarded /. lunatic, this is a good thing. It also makes EEE basically impossible.
Are there other signs that Microsoft is moving in this direction? Yes, there is. The iPad (and probably also Android phones and tablets) are getting their touch-enabled versions of Microsoft Office at least a full year before any Windows tablet or phone. Given the importance of Office inside MS, there is no doubt that abandoning their own platform as the "most important" one is a huge flag of surrender to realities.
This simply isn't the Microsoft of the 1990s, and that's a good thing. No matter what the paranoid nuts go on about.
Oh, and as the "only" other managed software development environment, we should all be happy. C# and .Net is more than Java ever dreamed about being, and more than Java ever will be as long as Oracle uses a community process to manage the development. To me, a combo of .Net on the server and Angular and (at the moment, but that stuff changes all the time) Ionic on the client is fantastic. Cordova makes my life a good one, and .Net on the server blows Java out of the water every day of the week and 22 times on Sunday. Speaking here as someone being part of a team that delivered enterprise software (had it deployed at many customers) on the Java platform back in 1997-98 or so. JDK 1.0.2.