that it can be abused? Microsoft could find out that your W2k or XP install has a dupe CD-Key, and then prompt the update to install a "special" update for those machines that have dupe CD-Keys. Sort of an Anti-Piracy measure.

"Let's see, how can we mess them up? Make one update that messes with the dock, and another that hard boots the machine 33% of the time that a program is closed."