AC Delco also has a clear coated rotor that covers the whole rotor even the rotor facing where the brake material makes contact. And the brake pad just wear off that facing/coating during normal driving.
I think the consensus is is that the AC Delco (and NAPA) versions are just private-labeled rotors from Raybestos' RPT line. The Raybestos units are less expensive too.
I put these on my wife's car and am going to be putting them on mine soon. Your comment about the entire rotor being covered and only getting the pad-contact area worn off is correct. That's an oversight with "painted" rotors - they leave the entire pad face unpainted but no brake pad covers that entire area. What's left unpainted and not contacted by the pads will rust and isn't that (part of) the point of these rotors ?