Brian is absolutely correct. I worked for many years for a major electrical manufacturer. We had hoped to run the new version of these ungrounded residentials on one of the grounded automation lines by making a cover with the ground holes filled in (plus leaving out the ground contacts and the ground screw tab and screw). Very quickly we ran afoul of the NEMA configuration standard. You will notice that the parallel slots on the ungrounded are more toward the center of the duplex profile than the same slots of the grounded. As Brian suggested, the low volume for these ungroundeds as replacement-only made the tooling investments unjustifiable. I had the unhappy task of adjusting the factory costs of these ungroundeds upwards to reflect non-automated assembly.
