This is a very important point. The obvious strategy for Microsoft is to open up enough of the platform to allow it to proliferate, but keep enough of it closed

This is a very important point. The obvious strategy for Microsoft is to open up enough of the platform to allow it to proliferate, but keep enough of it closed to give their implementation the edge. If you were hesitant to invest efforts in the .NET platform before this announcement, and you depend on the high level APIs, you might have more reason to worry now.