Blizzard blew it from the moment they started downloading/syncing their games via BitTorrent - using their customers bandwidth to support games that they paid for.
How exactly did Blizzard "blow it" with this design decision?
Using their customers bandwidth to take off some load of their own patch servers during peak times is (imho) a pretty good use of BitTorrent. You can also quite easily disable this feature in their launcher app.