I don't think the incidence rate is too high. Flt crew can't see what/who is around the aircraft so SOPs usually stipulate requesting clearance from ramp to release brakes. I'm not saying it doesn't happen accidentally due to miscommunication but to deliberately try and fool the system? Any capt with that type of attitude at most majors would be asking for trouble, not to mention a rather unpleasant reputation among the rampees.
I'd like to see the forum where they state that practice is commonplace.