I read it in 2013, and it's probably earned me at least $100,000. That's being veeeery conservative.
Not everyone will have that experience, of course. I had an existing book series, and Authority gave me an idea for how to repurpose it into a larger business.
As for the package on his site: he probably wants to avoid support. You get a lot of it with a $20 price point, and as he wrote in the article, he's focussing on converkit. Whereas with the amazon listing, amazon handles all customer support.
(I learned that lesson with my own books. My amazon royalties are smaller than my overall business, but I'm still very glad to get them, because there's basically zero admin work required.)