But old PowerPC macs weren't typically multicores, and even when they had multiple CPUs, people rarely programmed threaded software for them. Memory ordering is completely transparent to a single thread -- it's only when you add more of them that you start to have problems.
Only the most expensive PowerMacs had multiprocessors; iMacs, PowerBooks, and iBooks vastly outnumbered those with top-end PowerMacs. Which also meant there wan't much point in writing heavily threaded programs unless specifically targeting high-end users.
