I found being in Playstation Plus has gotten me into the downloadable habit, even though I almost always buy games when they are on sale, but again, that keeps me away from the used games from Amazon and Gamestop.
From a financials standpoint, this makes the same case as SaaS software does -- recurring revenue stream, predictable income, and so on.
It also increases the consequences of getting banned by the XBox staff. Not only can't you go online for multiplayer, you can't play your subscription games either.
Sounds like a classic case of "this is feature not a bug". With this system the stakes will be significantly raised for those who are verbally abusive on Live. Although admittedly I don't know if increasing penalties for the riff raff will improve their behavior or not.
Part of the catch may be that they are bidding to cut out used game stores like Gamestop. Through this system, they get paid directly, diminish the supply of used (substitute) goods and can combat rental outlets like Redbox and Gamefly, by having less capital costs.