Yes, they absolutely can ban your account for no reason whatsoever. But that would just be bad business. At the end of the day they want to keep as many subs as possible but they also want to get rid of people who make the game environment less fun (because when the game is less fun, other people leave).
So the reality is Blizzard aren't interested in permanently mass banning everyone who has made a few gold from exploiting a bug. They are after the big fish. For the smaller fries, if they can give them enough of a fright to deter them from trying anything like that ever again, that is perfect.
Which is not to say one should ever be complacent about these things. Making an example out of a few relatively minor transgressors is also an effective deterrent against others trying the same thing.