What does a replenished do, anyways? And by that I mean chemically.
A replenished developer system recycles most of the developer after use. An amount of either a specific replenisher or fresh developer is added to maintain the developer's strength. An example would be D-76 used with replenisher D-76R. It's economical but there is some change in the developers action after each replenishment cycle. People tend to either love the idea or hate it.
A rock pile ceases to be a rock pile the moment a single man contemplates it, bearing within him the image of a cathedral.