It's quite mind-boggling; nobody is really doing it on an industry-scale level. Every video game developer has their own way, all of which have their own problems.
It is a very hard problem. Blizzard actually came up with a very good system, but it's not in a state where it can be commercialized or open sourced.
I actually think whoever comes up with a system which solves these problems in a clean and consistent way will be sitting on a little revolution for content distribution.