A successful man in the middle attack over the public internet is very involved. When you change your Battle.net password and remove an authenticator you have to put the authenticator code in TWICE. A simple man in the middle attack would only capture the single code a person used to log in, and you wouldn't be able to compromise the account.
A successful account would require you to own someone's box, watch their battle.net login attempts, fish out the authenticator code and use it within the valid window (about 45 seconds in my experience) to log in to battle.net, then suppress the legitimate login response and inject a falsified bad login message (or pass a falsified login attempt to blizzard and pass the legitimate response back to the victim) to get the victim to enter their authenticator code a second time, at which point you could change a password and remove the authenticator. If you're going to target an attack this specifically you may as well go straight for the bank accounts.