Fair point. I guess I'd overlooked the fact that some people will be fortunate enough to have never yet seen such vile situations. It sort of shocked me because at 40 and (I think) streetwise, I've seen this sort of thing all too often, but you're right, even in my martial arts class, it kind of worries me when some of the students (particularly the younger ones) are so full of confidence that their moves will always work.
Its like the other week, I was training 1 on 1 with a lad who is much younger than me, but much higher grade. He took out a rubber dagger, and showed me how he wanted me to attack him with it. I said "everyone knows how to defend against that move". "Oh really?" he asked, with a big grin, so I told him to attack me that way, I am a white belt. As he held the knife up, I rushed him, grabbed both his wrists and stuck my right foot behind his legs and pushed, all in one swift and rapid movement. I held him to stop him actually falling back, and didn't bother to explain that had I followed through, I would have fallen with him, using his stomach as cushion my knee from the floor. It might not be a formal move, but I've actually had to improvise for real in the past, and I know that works.
A couple more times, when I was attacking him in the way he asked me to attack, I'd get the angle wrong or something, and consequently his defence would fail, and he would tell me I'd done the attack wrong.
I have no doubt whatsoever that martial arts training will help in a real situation, but you're right, people need to know that when its real, club rules mean nothing. Martial arts is useful as a means of improving reflexes, stamina and flexibility etc, and 'muscle memory' will mean that any blocks and strikes you do are more likely to be executed well, but improvisation is one of the keys to walking away (or running away - I've fought for my life long enough to find the opportunity to leg it more than once).