Except it isn't his property (as stated in the EULA, any and all characters, items, etc, are property of Blizzard) and Blizzard had nothing to do with it being stolen, nor could they have prevented it.

I'm actually going to change my previous suggestion. I don't think they should help anyone who gets their account stolen, unless they purchase an authenticator and link it to the account that was stolen. I think that's completely fair, and more than Blizzard is even obligated to do.