AFAIK it's not relevant even on OS X. Software controlled in this case means that CPU throttling is done on driver-level. The CPU driver throttles CPU down when CPU usage is low and back up again when it gets high. Applications itself does not have to support SpeedStep, PowerNow! or Cool 'n Quiet technologies. This becomes only somewhat relevant with games that use hardware auto-detection to determine optimal in-game settings. It is common that in the case of CPU's such auto-detection checks for CPU clock instead of CPU family and model, in which case it is possible that auto-detection thinks you have poorer CPU than you really have.