They should work on apt-diffs first which Redhat already does. The torrent idea may not be practical because your machine would have to be running the torrentable-apt-get to act as a peer. I doubt many people would want to leave that running and the short 10 second connections would not be enough to sustain the swarm.
You can also torrent the CD and create a sources.list entry to use the CD as a source, which will let you upgrade most packages (though obviously only packages that are on the CD). You can even loopback-mount the ISO, so you don't need to actually burn it.
