There will always be attempts to automate stuff. Some kid can always fire up his vc++ and send some keystrokes and mouse-clicks to another application (not even talking about hooking into the app or binarys itself).
The only question always is, how aggressive a company wants to fight that.
Are they implementing a client-detecting attempt (first line of defense)?
Are they implementing a server-side detection?
Are they implementing plausibility algorithms, creating some kind of "captcha codes" on suspicion?
In the end, you'll never be able to stop software to interact with other software one way or the other. The only question is, how much you want to take the jam out of their donuts and annoy them.
If you doing it well, bots won't be viable enough to sell. At some point, they even won't be viable enough for the coder himself. But obviously, that requires, time, effort and money. All things Blizzard is not really famous for to spend.