I've suddenly realised what Microsoft is talking about! We've been looking at it from the wrong side.
The UAC is not there to help keep users secure. If you think about it, it is there to allow developers to keep writing the same security-busting code they have done since Windows95.
Take a leaf out of Apple's play-book. If you don't keep your code up to date, then you don't get to play.
Please watch and understand this: http://www.microsoft.com/emea/spotlight/sessionh.aspx?videoid=993