The system enables strong second-place candidates to stay competitive and extend the race - as long as they don't run out of campaign money.
"For people who want a campaign to end quickly, proportional allocation is a bad system," Devine said. "For people who want a system that is fair and reflective of the voters, it's a much better system."
Another big change was the introduction of superdelegates, the party and elected officials who automatically attend the convention and can vote for whomever they choose regardless of what happens in the primaries and caucuses.
Much has been made of the superdelegates this year because neither Obama nor Clinton can reach the number of delegates needed to secure the nomination without their support.
A more subtle change was the distribution of delegates within each state. As part of the proportional system, Democrats award delegates based on statewide vote totals as well as results in individual congressional districts. The delegates, however, are not distributed evenly within a state, like they are in the Republican system.
Under Democratic rules, congressional districts with a history of strong support for Democratic candidates are rewarded with more delegates than districts that are more Republican. Some districts packed with Democratic voters can have as many as eight or nine delegates up for grabs, while more Republican districts in the same state have three or four.
The system is designed to benefit candidates who do well among loyal Democratic constituencies, and none is more loyal than black voters. Obama, who would be the first black candidate nominated by a major political party, has been winning 80 percent to 90 percent of the black vote in most primaries, according to exit polls.
"Black districts always have a large number of delegates because they are the highest performers for the Democratic Party," said Elaine Kamarck, a Harvard University professor who is writing a book about the Democratic nominating process.
"Once you had a black candidate you knew that he would be winning large numbers of delegates because of this phenomenon," said Kamarck, who is also a superdelegate supporting Clinton.
In states like Ohio and Pennsylvania, Clinton won the statewide vote but Obama won enough delegates to limit her gains. In states Obama carried, like Georgia and Virginia, he maximized the number of delegates he won.
"The Obama campaign was very good at targeting districts in areas where they could do well," said former DNC Chairman Don Fowler, a Clinton superdelegate from South Carolina. "They were very conscious and aware of these nuances."
But, Fowler noted, the best strategy in the world would have been useless without the right candidate.
"If that same strategy and that same effort had been used with a different candidate, a less charismatic candidate, a less attractive candidate, it wouldn't have worked," Fowler said. "The reason they look so good is because Obama was so good."