Yea while this is certainly true, especially if they can't sell individual games on a regular basis, but as we should be well aware of now, the whole monthly service thing, really only disincentivizes quality game creation.
Lets be real, if MS could sell games at retail, going the service route would only lead to them losing money in the longrun, as would pumping in a insane amount of money to drop into a pool of games, that all share the same fee.
If Sony or even Nintendo went this route, as bullish as MS is, they would make so much less money, Sony would downright go under(do to the Playstation division having to support all their other divisions), and Nintendo would be a lot smaller then they are, although probally not to the point of struggling(their IPs are too valuable, everyone would suck it up, and pay for their service).
Sure MS has windows, and server services, so as a company it wont effect them either way, but yea this move only makes sense, if you can't effectly sell games otherwise.