I agree with everything you say about attempting to create a game without taking advantage of the platform specific features from the ground up. If you want to make a great interactive experience that is the way to do it.

Taking this presentation literally the only games that could survive a deployment like this would be the most basic of games. The inputs of PC and console are rich enough to be able to translate without much pain. Adding a mobile device that may not even have proper buttons or multi touch and will most likely have limited screen real estate is going to seriously limit what can be accomplished on the other platforms. At this point you would be developing for the lowest common denominator platform.

For a lot of game companies this is acceptable. The kind of video game mills like EA or others that specialize in titles based on movies, TV shows, or toys can get away with this. Typically their target audience will not care or can overlook the concessions that will ultimately be made. The strength of their tie-in may be enough to generate a profit on the sales.

However, I think what MS is trying to do here still has value. Perhaps treating this as a panacea for the pain of cross platform mobile development is overstating the issue. In the end, this and solutions like it http://unity3d.com/ make developers drool. The entry cost for multi platform development is being lowered which is ultimately a good and democratizing force.

MS began this with their XNA initiative which I am a big fan of personally. Microsoft has had its issues with user experience, but never let it be said they neglect their developers. I don’t pretend to believe they do this for selfless reasons, but their tools are compelling.