You are right, this hasn't been how Macs have worked the past--

This jack is described as "Combined optical digital audio output/headphone out (minijack)" on the Apple web site, so it seems that it can output either digital or analog audio. There must be a System Preference file setting to determine what mode it is in.

Traditionally, you would need to access both the Audio out and the DVI out ports if you were to play a DVD to an external monitor.

Specs on the DVI Port:
DVI video output to support digital resolutions up to 1920 by 1200 pixels; supports 20-inch Apple Cinema Display and 23-inch Apple Cinema HD Display; supports coherent digital displays up to 154MHz; supports noncoherent digital displays up to 135MHz