Admittedly I'm cynical, but how is a "primarily responsible person" different from a lead developer? It feels a bit like you're just calling things different to avoid manager-like names.
Who assigns the shit task to whom?
Added: That's a little too glib, sorry. Let me try again: From my perspective, if there's something that needs to be done at GitHub there are a few possibilities:
1. It needs to be done and it's getting done,
2. It needs to be done and it's not getting done, or
3. It's bullshit.
Cases of #3 become obvious pretty quickly. The best evidence: Searching for ways to make someone do it because nobody stepped up.
Cases of #2 can happen for a bunch of different reasons, but malice, apathy, laziness, or incompetence are the least likely ones. The most likely: Not enough hours in the day or not enough people with the knowledge necessary to be worried. No matter the reason for #2, someone at GitHub who is worried will generally try to get others to share their priorities, by persuasion, by hiring, or by prototyping.
Or occasionally by just jumping up and down and wailing.
We call them project champions. I work in an agency model, so we have many clients who have many projects. The project champion usually knows the client, their wishes, etc - acts like a product owner (if you're familiar with the term from agile methods).