Clearly each party can set up whatever rules they want, including the establishment of super-delegates, super-duper delegates, maybe delegates apportioned by ethnicity or religious affiliation. I don't think there any legal/constitutional issues concerning the means used to select the party nominee.
As I understand it, the Democratic Party chose to have these super-delegates for precisely the reason outlined by Rustic23--to allow the powerful upper echelons to tweak the system in order to select the most electable candidate if the popular voting was relatively close. We'll see how well that works. Clinton, for all her baggage and high "negatives" with many people, is a known quantity who is far less likely to go disastrously off-course in some unpredictable way. She's a safer bet, and Democratic Party "Lifers" and big-money folks prefer safe bets.
If Obama wins the popular vote and Hillary is the party's nominee, then one would expect there to be quite a backlash among his supporters. Likewise (but to a lesser degree) if Hillary wins by virtue of getting the Michigan and Florida results included despite the earlier agreements. McCain might win some of these people (though probably fewer if Obama is offered and accepts the position as Hillary's running mate).
I don't know if African-American voters would abandon the Democratic party-they've been taken for granted for a long time and yet they stay aboard. Still, this could be the real wake-up call. It might even set the stage for the right dynamic young black Republican to make some headway on the national scene. I don't know who that would be, but I'm sure there's somebody out there..
Won't it be great when race doesn't matter anymore? We're getting there, but far too slowly.