To Quote one of the community managers on the official forums
"This isn't our first rodeo. We have been actively monitoring for exploitative behavior since the game launched and taking action as needed. We haven't been very vocal about that process (though we have made a few announcements for larger ban waves in the past), but that's something we'll be working to change and improve upon going forward."
In response to this thread:
Diablo III Players Banned for Botting - Forums - Diablo III
So ban waves aren't real, eh?