You obviously weren't involved in the beta process.
It's not EXTERNAL p2p I'm talking about, blizzard's very own downloader is P2P. You download from peers, and when you're done the game continutes to run the client in the background uploading the content to more people. In theory this is good because you won't have as big of a slowdown from the rush of people downloading directly from limited servers. Once it's saturated through the community the downloads are fast. HOWEVER, the downside is that it's constantly using your connection without you knowing, and it affected the game's performance in single player which IMO isn't right.
In short, a lack of information turns your smartass post into a dumbass post.