The strategy seems so unclear here. Is the expectation that all casual games should be written in HTML/WinJS for Windows 8 Store Apps?
I would be happy to see MonoGame to be more officially supported by MS. MonoGame needs investment - like removing the dependency on Game Studio and better support for Windows Desktop based apps. How about Microsoft open-sourcing XNA and so that Xamarin can pick it up? Remember, XNA still doesn't support TouchPanel properly on Windows 7/8 desktop apps. It really looks like development has stopped.