All glass is NOT the same. The main difference is that your windshield is laminated and the other glass in your vehicle is tempered glass http://www.autoglassnj.com . What makes the windshield unique is that there is an extra piece of vinyl in between two layers of glass. The three pieces are laminated together in a special oven called an autoclave where heat and pressure is applied to the glass.
Oftentimes when a small object such a rock or piece of debris strikes your windshield, only the outer layer breaks. This is the reason it is possible to repair a rock chip in your windshield. As long as it does not penetrate through the layer of vinyl, it is possible to fill the chip in with resin. If the glass does shatter, the windshield is designed to keep the glass in place so that there are no broken pieces of glass. They are designed to stick to the vinyl interior lining.
Another reason your windshield is laminated is for the front airbags. Airbags deploy at extreme force, sometimes in upward of 200 mph. The front seat passengers crash into the airbag 50ms after a collision. The triple strength of the windshield is designed to keep the airbag in place all while keeping the passengers from being ejected from the vehicle. The windshield is also an important structural component which adds strength to the vehicle’s roof. The windshield is actually what helps keep the roof from collapsing on passengers in the event of a rollover. Without the windshield being so rigid and strong, it would pose an increased risk in the event of a rollover.
Tempered, or heat strengthened glass is generally used for all the other glass in the vehicle. Tempered glass is put through a special process where it is heated to extreme temperatures, then rapidly cooled. Tempering the glass makes it much stronger.
Another difference between laminated glass and tempered glass is the way it breaks. We have already discussed how a windshield breaks, but tempered glass is designed to do the opposite. When tempered glass breaks, it disintegrates into very small pieces of glass, similar to the size of rock salt. There will be no large jagged pieces of glass to injure anyone in the vehicle. The door glass is tempered mainly so that there is an exit point in case of an emergency. If a vehicle is submerged in water, or has rolled over, with the glass being tempered you can break it and safely exit the vehicle. The windshield is designed not to break so you will not be able to exit the vehicle that way.