Seems as if the Democrats change their rules for nominating much more often than the Republicans.
Back in the 50's the nomination was a combination of primaries and favorite sons and smoke-filled rooms. The 1968 convention with the Mississippi controversy over seating the black Democratic delegation resulted in changing to dominance by primaries. Then in the early 80's the pendulum swung back by creating the super-delegates to provide more "adult" guidance to the party. Now, after 2016, the pendulum has swung again towards primaries.
It's interesting to me, as a supporter of Amy Klobuchar, to note she does a lot better in accumulating endorsements from party figures than she has done in polling. That leads me to speculate that the switch away from super delegates may wind up depriving her of the nomination.