Thats a good point, in reality if they did go for the Ban by IP method, there are plenty of "get out's" here in the UK, BT (largest telecome provider) have rolled out in their routers an option to allow other members of the BT network connect to the internet through your connection..
I woulod boil down to the point of someone having the balls to stand up to Blizz and trying to bluff their way out of it.. It's not really worth the cost to Blizz to involve legal people just over a ban ...