I also have a a less then perfect windshield I was wanting to get polished,,,went to our local windshield/glass shop and asked them about getting it buffed out.
They said the same thing ,,that they used to ,but quit polishing glass on account of getting distorted. I didn;t ask ,,,maybe they were trying to get deeper scratches out or something,,but it kinda discouraged me so I think I will just polish glass by hand with nonabrasive polish and live with it !