Yeah ... that's pretty common, actually.
I guess that the auto mfr's thought that the motoring public would be intelligent enough to know that one you hit the lock in one direction and the drive belt started to squeal, that it would indicate that they had the wheels turned as far as they were going to go. I suppose they also thought that the driver would recognize this as an audible clue, and learn to relax his/her death grip a little ... apparently not!
The thing to understand here is that a power steering pump is nothing more than a simple hydraulic pump that provides a pressurized flow of fluid. When the steering box senses "high effort" (a specified torque figure at the input shaft) it opens a valve which allows pressurized fluid to enter and provide steering assistance in order to reduce driver effort.
So when you are holding the steering wheel at the lock, the valve in the steering box goes wide open, and the pump "goes for broke" as well.
Thank goodness that the engineers installed a releif valve inside the pump that allows the pressurized fluid to by-pass. This prevents the pump from locking up solid and either stalling the engine or burning the belt right off. If the belt is not tight enough, perhaps it starts to slip before the releif valve cuts in ... and the belt squeals. The oscillation of this bypass valve also makes a high-pitched sound ... again ... another audible clue.
I can't thelp but think that "forcing" the wheel also puts undue strain on the steering linkage as well.
I think that the more modern vehicles, equipped with rack and pinion steering have been engineered to be a little more idiot-proof. 4-cylinder cars also have a pressure switch / throttle kicker setup so that turning the wheels doesn't stall the engine.