Fred, I think the confusion is stemming from his observation that there are three prongs on the male outlet side of his Denon supplied, detachable power cord and also three holes on the female end of his power cord
but
the receiver itself was built with only two male prongs to plug the cord into. The ground pin is not present on the receiver to plug a grounded cord into.

I can see why he would ask the question.

With great power comes Awesome irresponsibility.