The easiest way would be to encrypt the addon store on the user's hard disk. MS could still install addons stealthily, but they'd need to violate the DMCA to d

The easiest way would be to encrypt the addon store on the user's hard disk. MS could still install addons stealthily, but they'd need to violate the DMCA to do so, and I can't see even MS being that willing to risk the legal issue just for an addon.