The Democrats have a very fuckedup system.
Since it's a private political party, and America is NOT a democracy (anyone who says it is is either simplifying the process or doesn't know the constitution), the primaries are only a part of the selection process.
A super delegate is one of the voters who decide who is getting the nomination. The primaries DO NOT ELECT the nominee. It's funny since the republicans use a democratic process and the dems use a more republican process, but then the names never really fit the idealology. The super delegate is a misnomer, since all delegates don't have to listen to the vote. Even though Obama and Clinton *have* pledged delegates, they can vote the other way just as easily. A super delegate votes on their own personal preferences. They are political leaders, representitives, past leaders (Bill and Hillary are both super delegates), governors, etc.
Superdelegates will decide this. Obama has the votes, but Hillary is snatching up the big important states. This is chess, not checkers.