In my experience, there are enormous differences between popular and
classical music concerts. Popular music concerts depend on a (perceived
or real) direct, personal connection between the performer(s) and the
audience members, and among the audience members - a sense of common,
group experience. I believe this feeling far outweighs the choice of
programming and has more to do with performer charisma and image,
atmosphere, and complex sociological stuff like group identification
(demographics), (implicit) political/philosophical climate, etc.
Incidentally, I think if one fully understood this difference, one would
go a long way toward understanding the apparent decline in popularity
of classical music.