In one of their presentations they mentioned "instant start", i.e. it downloads just enough to get you started then downloads the rest in the background.
Its probably the same streaming tech office 2010 home and student uses. It basically makes it unusable. Every time you click something it lags for 30-40 seconds while it caches dlls. Horrible tech.
I doubt its the same tech as the code to do this in a game would be totally different than the code for a desktop application. There's a big difference between JIT downloading and prioritizing so that you can start the game. I swear some people will find any reason to get in a shot against MS.
