What's wrong with the refactoring tools and debugging capabilities included in the Express edition?
They suck. Seriously. Try Resharper. It makes Visual Studio almost as good as Eclipse. What exactly does C#/XNA have over, say, C++/OpenGL (or even C++/D3D or C#/D3D)?
Automatic garbage collection? XNA doesn't seem to have any advantage over Managed DX, except perhaps speed. I'm guessing Microsoft are going to be pushing XNA fairly agressively soon, possibly to the point where DX10 can only be utilized through XNA.