I don't think that it really had any effect on whether or not people hacked on closed battle.net. They could just as easily hack in single player. It's not the same when everyone else is using the same hacks. People use hacks on closed battle.net to gain an advantage over others, because they are assholes.

They'll probably have an open battle.net, though. The whole point of open battle.net is that you can play your single-player characters there.