Sad, but true.
Microsoft would not receive a direct income from such a service, but it could be more indirect.
A lot of people are in this situation I just described and if they would have a service like that one available, some people who were thinking of going the sony route might even change their mind.
And why not sell this service seperately with some sort of Windows 8 Gaming edition?
That way you can request a bit more, just for this service.
People could continue where they left of, gathering more points, and maybe even cooperate with friends who are still playing on the xbox. (coop I can see, but competitive might be a bit hard with mouse vs controller)
The part of buying one game and being able to use it on console + pc is probably too far fetched, but just the service could be beneficial for both microsoft AND the developer (if they need to buy the game twice)
A friend will come bail you out of jail at 3 A.M. but a best friend will be next to you saying " Damn that was fun"