If the delegates were to be bound to the candidate who recieved the most popular votes, the most elected delegates or the vote of their districts, then they would serve no purpose. The system was devised so they could have influence in the decision making process.
These are the rules. The rules have been such for a long, long time. It is a little later for Pelosi, Obama or anybody else to complain about it now.
There are plenty of other byzantine mechanisms on both sides to let the party leadership swing a close race. Both parties. In many primary states and most caucus states, delegates won't be formally chosen until the state party conventions, which are held in the summertime when the handwriting is pretty well on the wall.
The rules have been such for a long, long time.
Only since about 1980, or maybe even 1984, IIRC. Before '68 or '72, most of the delegates were not allocated by primaries or caucuses, and most candidates did not contest many states. The primary process is not enshrouded in tradition going back to the Founders; it's been constantly tweaked over the last 40 years, 50 at the most, and the parties are still working on the balance.
The only reason anyone cares is the same reason the American public suddenly discovered the Electoral College in 2000 -- it hasn't been this close before.
Though everyone is hot and bothered over the superdelegates right now, if Obama emerges as the clear front-runner in citizens' votes after next Tuesday, I'd expect the superdelegates to fall right into line. A floor fight is not good for the party, and a weakened party is not good for them.