If it is the case that I have to pay to have privacy on Github, then it imposes a privacy-rich versus privacy-poor dichotomy which I am uncomfortable with. Now I know as far as these things go (GH can be subject to National Security Letters), that GH is not really absolutely private. (Backdoors into people's 'secret' GISTS anyone?).
GH had an opportunity here to change their business model so that free users can avail of private repos, and GH could still manage to bring in revenue. GH primarily makes the bulk of their income from what I call 'stakeholder accounts'. That is; those companies who simply couldn't function correctly if GH didn't exist. It is in these stakeholders that there is a symbiotic relationship of revenue for GH, and value for the stakeholder(s).
There are very little lone private individuals who have that kind of symbiotic relationship, and so at least give these low income users the same equal rights of privacy as behemoth tech organizations. It makes sense.
In terms of how GH gets revenue from these users, there are countless other ways to do this instead of relying on the monolithic device of a premium subscription model. Offer paid licenses for their proprietary GH clients. (A one off payment of $20.00 for the GH Windows client is something I would actually pay money for)...