But then the conversation stops within days because, the fact is, hosting your own git servers and getting people to actually use them is a huge pain in the ass. More simply put: people just like using GitHub.
Furthermore, GitHub's a business. They're selling private repositories. They do open source quite a bit of code, but they're not going to open source their actual product.
I just wanted to point that now that you guys are well stablished and have huge impact in the open source community, adopting a more open approach with your end users can be very beneficial for both, GitHub and the user base. I'm sure that lot of people would contribute to your codebase and thing like this: https://github.com/dear-github/dear-github would be less frequent and notorious.
But if the enterprise edition is really the source of income, open sourcing it doesn't have any sense. I agree on that. Maybe, another way to be more open to contributions from the community ? I dunno
Given that this is the case, I fell like GitHub is entrenched enough that they could open source their codebase and not lose any customers. People are paying them for the convenience of someone else hosting their git repository.
But yes, most of us are most comfortable with the central repository model.