John, if I remember correctly, the Australian CAA brought out a CAAP (Civil Aviation Advisory Publication) on weights, where they listed different weights for different sized aircraft. The idea was to stop a guy on a Navajo using an "airliner" 75kg weight when he knew he had eight 100kg passengers on board.
In any case, the regs were written "thou shalt not fly overweight" - use of average weights did not absolve the pilot from that dictate.