How odd, I'd never even heard of such a thing. I wonder if it has to do with minerals in the water?
I have 3 sets of dishes, and use them all, all the time. Orange lusterware that came in soap boxes in the 1950's, Corningware I've had since the last 6 or 7 years, and Royal Dalton bone china which I've had for about 30 years. No marks at all on the Corell, I see scratch marks on the Royal Dalton and lusterware, but have to hold them at an angle to the light to see them. No dark marks at all.
We have minerals in the water here, but the water is naturally very soft.