The schelling point for an ecosystem is often just as important as the protocol.

Git is the protocol; GitHub is the schelling point.

The schelling point is where people go for discovery of new things.

Without it, you don't know where the other good things that speak the protocol are.

GitHub and Git both need each other.

Git's protocol design (with extremely lightweight branching) made a thing like GitHub's forking possible.

GitHub's ubiquity locked in git as the obvious protocol to use.