It needs drivers, they are just the same as the audio jack. At least in my computer (not apple), the same board that drives the audio jack is, at the same time, providing output for the optical plug without any special software.

I've never used an external DAC, but it seems that the parent is weary of companies fucking it up with the usb drivers (or the firmware in the device) and introducing delays or artefacts in the audio stream. An optical to audio converter is easy, probably any third year EE could produce a working prototype.

Ok, to be clearer, an optical connection uses the drivers from apple and will always work well whereas I've seen some usb dacs that used custom drivers and would fail (example AT-HA90USB)