I'm a member at FS.IMHO I would challenge this. In all my classes I have been taught, IF you have to use a defensive weapon to save your life or a life of a loved one that you shoot until the threat is eliminated or stopped. (LEO and Civilian)
No where have I encountered instructions stating do not shoot anyone in the head to stop the threat.
What they teach in the basic classes is two to the chest (controlled pair, not double tap; not the same thing) and if that doesn't do the trick, go to the head, the rationale being that if the first two don't stop the threat there's no reason to believe more shots to the chest will do so. The doctrine is the same in the rifle classes. I'm not much of a shotgun guy, and haven't taken a shotgun class, so I can't speak to their doctrine there. When I took the rifle class with a .308 they were fine with only one to the chest.
In the more advanced classes that goes out the window, and they say shoot 'em as much as you think they need to be shot. (They use photo targets, one of which is a brush-headed guy leveling an AK. Last time I was there they popped that target up at me and it actually scared me a little - "Crap, AK." I gave the SOB 8 or 9 rounds, which I think he deserved, and got hearty approval from the instructor, a Salt Lake City cop.)