According to Microsoft (Herb Sutter talks at build), as hardware gets more mobile (tablets & phones) we are suddenly facing hardware that lacks performance compared to our laptops and PCs. This makes the performance of software more important. A less performant language may come up against the hardware's performance boundry sooner.
C#, although considered higher rated in productivity than c++, generaly runs at a performance handicap to c++.
Since it is felt than in the coming years performance will outweigh productivity in software development due to hardware going mobile, Microsoft seems to be putting c# game development on the back burner and turning the heat up on c++ game development.
It is unclear whether we will see another update to Xna. Most likely Xna development will not be a part of windows phone 8. Since Xna was not invited to be a part of WinRT, it leaves us wondering if it will be invited to the next xbox.
I'm sure the AAA game studios are content using c++ for the forseeable future.