And I should have clarified, I meant that MS isnt supporting XNA, which I think was one of the main reasons C# gained traction. It might very well continue to be used in Win8 applications, but since this is a game development forum I'm thinking mostly of... game development. As far as game development, c++ will continue to be the standard.
C++ isn't really used on its own, I like the language and use it but it isn't as super powerful as people claim it to be nor is C# another stupid slow managed language.
Majority aren't always right, I don't know about the game industry but I know of other major industries and typically following the bandwagon is rarely to do with productivity, it is more to do with shareholders / business managers lacking balls, and lets be honest here considering every other game released in the last few years is an ''upgrade' of some other game, I doubt the game industry are any different from other industries.
Besides you already said
"Just because something is widely used now doesnt mean it'll be widely used in the future."
Surely this must also apply to your C++ comment too then ;)
I say all of this as someone who uses both C# and C++ heavily and daily. Personally I always thought C# gained popularity because of how easy and efficient .NET was to make applications, work with databases and make websites.
Not to mention, companies with a large codebase may be reluctant to tear everything up to move to the latest trend in programming languages, that's sometimes too little gain for too much work (and work that potentially will be a nightmare to test). Hell, at work we still have numerical engines written in Fortran, even though our primary application development is in C# (and bits of C++/CLI here and there).