There's nothing wrong with showing gratitude from time to time, even if it's for a for-profit corporation if you truly appreciate what they do.
That's cool and all, but wasn't the motivation for the first letter the lack of humanity from GitHub in communication with the userbase?
I don't think they deserve a cooing public letter to reassure them on the basis of humanity after they've decided to give "empty response or even no response at all" to what read like perfectly reasonable attempts to communicate with them.
I'm entirely willing to use person-to-person social standards for a company. I'll start with a trust-but-verity attitude, because leveraging a double standard in customer facing business is often a way for companies to take advantage of customers. Once they show they're not interested: fuck 'em.
> I own you no shit
GitHub might owe them nothing, but it's in their own interest to address and resolve those issues and not just stash them away somewhere. Their biggest selling point is the great UI and the userbase. If the later becomes frustrated because issues with the former don't get resolved, that might be a huge problem for GitHub in the future. Today, there are viable alternatives after all.