Comment by cosmic_cheese

On top of this, they started encouraging adoption of multithreading and polished up the APIs to make doing so easier even in the early days of OS X, since they were selling PPC G4/G5 towers with dual and eventually quad CPUs.

This meant that by the time they started pushing devs to pay attention to QoS and such, good Mac apps had already been thoroughly multithreaded for years, making it relatively easy to toss things onto lower priority queues.