In Ye Olde Days at least the main repository was something you visibly had to maintain. The original author A would set up a project on sourceforge, and add B, C and D with commit access. (Indeed, I remember this being cited as one of the great advantages of git - it breaks down the two-tier society where you had an inner circle of authorized committers, and then second-class citizens who had to submit their patches). But it did mean you would do succession planning around it - if A got hit by a bus, someone else would have access to the One True Repository, and they could take over merging patches from outside contributors.

Ironically, github is making it easier to have a single central point of failure. Because it's so easy for the original author to merge patches from other repositories, there's no longer any pressure to give other people access to the "master" repository. Which is fine until the original author stops doing it (for whatever reason)