Excellent point--not really a lot of point in learning about the old church modes--

As for jazz, they use the word "mode" simply to describe a scale that starts on a different step of a given key than the fundamental--they usually bang away on one chord (say a C9, in the key of G) and you play your "Dorian" scale by bouncing around phrenetically between the A and the D, filling in the rest of scale notes according to your whim, to break up the monotony--you may also pepper the music with any sort of random noises that you can squeeze out of you instrument without actually damaging it(if you damage the instrument, it becomes punk rock)--