I just noticed that Apple must have changed the way they package App updates in iOS6.
My Garmin navigation app is normally a 1.3GB download and previous updates have taken forever. Today, I just got an update pushed out which took about 2 minutes to download and apply.
There is no way that downloaded 1.3GB in that time over Wifi so I believe they must now be sending updates as a diff style differential update, which will be saving them a lot of bandwidth and users a lot of pain... we no longer need twice the install space to download and apply an update, which is what used to happen.
This is a neat new feature I've not read about. The other being that updates no longer prompt for a password.