Not sure if this is the correct forum, but...
 

I'm curious. Say if a DVD has an "audio only" track in the "Extras", like my DVD of "My Favorite Wife", which has a radio show version from 1950 in the "Extras" section, is that audio "DVD Audio" or just standard MPEG2 video/audio, except minus video?

I'm going to give this one a shot:

If by "DVD Audio" you mean the high resolution format "DVD-Audio" then no, the track is not DVD Audio.

More than likely it is a Dolby Digital or wav. file on the disc. The music could be coded in MPEG format (without video as you indicate), but I don't believe most audio only sections are.

Someone more technically astute than me may say I'm full of crap (which is what I'm generally told anyway).