From a reputable, accredited university?

I think that's the slippery slope that the Prof in question is worried about. Right now, a PhD from the University of Manitoba should hold more value than a purchased one from a diploma mill. If enough of the requirements are waived, this may no longer be the case.

Unless he is referring to "honorary" doctorates, which are an entirely different conversation. These are sometimes given for reasons that may make it look like they were "purchased."