rvm (an open source tool for managing your Ruby environment) had a crowd-funding campaign: https://www.bountysource.com/teams/rvm/fundraiser
They collected all the cash they needed, the maintainer took a break for some time, and now they're working on the next major release.
If a website using https (HN) points to a website not using https (the blog), then the referer is hidden. So it's not something HN is doing specifically, it's just because one is https and the other is not.
Pay as you want for books is good idea, as long as you know what to expect. Good job on summarizing the outcome :)