Serious bikers know how to 'fall down' and how to react to the situation. If you try to fight some of the rolling and tumbling across the ground, you can actually hurt yourself more. If you are wearing proper gear, your skin is protected for some sliding and slapping around, and your key impact points are protected - like your elbows, knees, and head. It all works fine IF you don't get a really sudden stop in there, or run over by something (including your own bike). Problem with comparing that to a car is that you take away the open spaces to tumble on, and now are being shaken around inside a steel and glass box. No thanks.
Oh, and nobody goes THROUGH a windshield with 'just a few scratches'. I walked on a car hood once and fell and hit the windshield - and didn't break it. That HURT, and left me with some good bruising. Going through one at 45+ mph is NOT going to be a 'just a few scratches' experience. If you can hit it hard enough to break it such that you can pass through it, you are taking some serious damage.