I am not sure that's what people are saying. I agree, wind or opening the door, yes, that would be defective paint, and I have seen that before.
What I was imaging was handling and abrasive situations, like driving down the freeway behind a truck, tossing up dirt and sand.
Look at it this way. Examine your mouse, and keyboard. What does it look like? How dirty is it, scratched. If you have a MacBook Pro, look at the track pad. It's made of glass, but look how polished it is by your fingers, natural oils.
These things are going to happen to your phone, a black phone with thin layer of atoms thick black anodization.
My truck handles abrasive situations with ease. It has seen many dirt/gravel roads; yet, it is not pebbled with chips and scuffs. In fact, it probably isn't because the manufacturer had enough foresight to ensure the paint could at least withstand normal operation--i.e., driving.
In the case of a cell phone--holding, carrying, setting on tables, putting it in pockets etc.