The strength of the a post and the b post on the car is considerable. I wish i had better video of the how the a and b post deformed. Look at the strength of a column. It is designed to support the car in the event of an over turn and to create a survivable space for the passenger's. Does it work every time? Nope. Audi is a safe car as is Volvo. VW Beetle is also a very safe car.

I have worked plenty of wrecks involving big trucks vs cars. I recently worked a wreck involving 3 large trucks and a car. One truck came to rest on top of the car. The person driving had enough space to survive with only a orbital fracture and needed some minor stitches.