I like your book. Have read about a 100 times. Its good. But its not perfectly marketed. The title does not fit the book. You are not teaching Ruby on Rails per se, but web development and deployment with Ruby on Rails. There is a difference between the two. Imagine a beginner, who has no experience with actual web development, but wants to try out RoR to find out what the big fuss is. He/she finds your book, and starts reading it. Only to find out that he/she has to learn about n different things before learning how to include a field in a model. Its frustrating. I know because I went through it. Even though I knew git/heroku deployment beforehand, skipping over those subjects proved difficult.
Though you do make a good point in your first sentence. It does depend on the goals and the audience. But I think your audience is a bit too widespread. People who have some programming experience are too wide of a net. I think if it were sold as a book for people who havea bit of web development experience then your conversion rate would be higher (from free reader to paying customer).
Now, I'm not knocking on your accomplishments. My approach is merely from the business perspective of marketing you book and videos. Have you tested other approaches? If so, may you shed some light? I used to market/sell books on the web, and find it fascinating. If you wish to continue this conversation through email mine is in my profile.