Safety glass was designed by the wife of a Dr. She was in a car accident and got cut up really bad. It was then mandated that every car coming out of the factory had safety glass.
A lot of the older cars coming from Europe had a tempered w/shield just like the backglass and side windows. I've gone to replace one to find half the windshield still in place and the other side shattered. It was designed like that so if the windshield broke the other half could be seen out of. Try driving with a face full of glass.