Blizzard's World of Warcraft uses BitTorrent to download patches. The software includes a BitTorrent downloading client that also offers non-P2P downloads for those in environments that block all BitTorrent like traffic.
It is standard. I found the .torrent and have been serving it via a standard BitTorrent client for a while. Both a nice thing to do and my way of supporting legitimate uses of BitTorrent.
Well, almost standard. It appears that Blizzard's patch downloader ensures that there is at least one viable channel open outside of the BT traffic just in case your system can't reach any other system within the BT swarm.
It would be interesting to see the bandwidth charts for World of Warcraft BT traffic after a patch release. I wonder how it compared to to the infamous release of RedHat 9. The path is a lot smaller than a Linux distro, but I bet there are a lot more World of Warcraft users than RH9 users.