@shadling21: Yes, I do have my prejudices in favor of more modern forms of dance. Ballet gets millions of dollars in support. The same amount of support could fund countless modern dance groups. Even today, though, ballet is a sign of status, both for those who fund it, and for those who watch it.
Ballet relates to improvisational dance only in that they are both called dance, and they both require dancers to move in expressive ways. Improvisational dance is more open to ordinary people. It does not require dancers to contort themselves into unhealthy states. Although, they both help dancers get arthritis at an earlier age, I think balletic dancers get arthritis earlier. The stories they tell are also qualitatively different.
There are classical dances in ballet, and even contemporary dances seem to me to be more formalistic, if they don’t tell stories. Improvisational dance doesn’t have classics, unless you count a dance performed thirty years ago as classic (if you can even reproduce it). It can also get abstract more easily. It can be dance about movement or about a specific movement. I believe it, too, can be hard for audiences to understand.
I’m sure there are many other points of comparison, but I can’t think of them now.