This thread poses some interesting questions. One thing that I got to thinking about was where the complexity lies in classical versus jazz. In classical music, much of the complexity comes from having a large number of "voices" playing simultaneously (i.e., three or more violin parts, violas, cellos, basses, various woodwinds, etc.). Generally speaking the level of rhythmic complexity is fairly low. In jazz, on the other hand, there are usually a relatively small number of simultaneous voices, but the rhythmic complexity level is high.
I think that there are also some characteristics of the rhythms used in jazz that are rarely, if ever, associated with classical (as an oversimplified example - the use of syncopation in jazz).
