MS wants to control the Cloud. If Amazon or Google win the race for a game streaming service, MS will be very upset.
Sony is small potatoes, Nintendo is basically a non-competitor/friendly colleague in MS' eyes.
If MS is successful in getting the defacto game streaming service, they "win" (at least by their metric).
I think there is some merit to your hypothesis here. The thing about these big companies (like Microsoft) is that they often have access to leaked information that the rest of us don't have. Google is going to unveil new gaming hardware soon, but we really don't know hardly anything about it yet. On the other hand Microsoft actually may already know what this hardware is, and they have already taking steps to compete against it.
I expect things to become more clear when Google announces their new hardware.