I imagine whatever reason it was is now lost in the mists of time... (or some IATA conference in the 70s) but I would be as interested as anyone to find out why pretty much every airline just does the piece system to/from&through North America.

While we're at it, anyone know how come many US travellers carry vast amounts of cargo into the cabin? I had a laptop and one of those huge 20kg-monster-suitcase-on-wheels nearly clobber me when I opened the overhead on a NZ flight to SIN recently.. thankfully it missed me and fell onto the legs of its owner who had huffed and puffed and jammed it in a precarious position on top of my small rucksack carry-on into the bin..