While I can't say what chaps were originally intended to protect the rider from, wind, weather or road rash, I can say that both of us praise our chaps for protecting us when we were sliding down the highway last August. Deb's chaps had holes where the pavement abraded the leather clean through, yet her jeans and skin were untouched. My chaps were severely abraded at the knee, hip and thigh, yet I suffered no skin damage.
We have replaced our leather chaps (and leather jackets, gloves, etc) with new leather chaps, because they did an excellent job of protecting us in a crash.
ATGATT for us (before and after).