my drivers ed teacher drove that into my head almost 25 years ago now and as hard as it was to believe at the time I always followed it, and now my wife doesn't believe me. I suppose once she finishes school in july she'll end up taking some trauma x-rays and will learn for herself. All her clinicals so far have been in clinic type (non emergency) environments.
I've always known and followed the thumb thing. What gets me is people riding around with their feet on the dash/airbag. I've been whopped by an airbag, they're not friendly. If one goes off with someone's legs on it, I'm sure it will fold them in half, probably at the knee.