Back in the late 70s I would inflate the tires of my air-cooled (rear-engined) VW bug (per spec) at about 18 psi front and 30 psi rear... because the weight bias of the car and the tire technology of the time dictated that. So yes, I agree that weight bias is a factor in what the working psi of a tire should be. But spec'd psi numbers have their place if not to at least offer a starting point from which to work from.