Which is why it makes sense to distribute updates P2P. I'm a little surprised that nobody has already written an update framework that does this for desktop applications -- if the applications themselves are signed with a key contained in the original download then you can securely receive an update from any host, which means that each client only has to upload the package an average of once (i.e. it costs them on average a fraction of a penny in bandwidth), and the same for the original source.

Some games already do this because they're so large, but it would make a lot of sense to factor it out so that multiple applications could use it.