[mblake]

Off the top of my head, I think https://leanpub.com/ is similar to Hyperink. I think if you do a bit of Google digging you can find stories from authors who decided to self-publish with specifics analysis of their process (what they used, how much time it took, revenue analysis etc.)

I think the new blog posts that were added to the book serve as an incentive to buy it, probably a lot of the HN users were already familiar with Patrick and might've needed a little 'push' to click on the purchase button :) Just one of the possible reasons.