This advice is written from the perspective that writing is 100% of the project. Writing is 10% of the project. Writing a salesletter, a marketing site, linkbaits, and obsessive promotion is the other 90% of the project. That is time debt that I take on as soon as I sit down and say "OK, I'm going be become an author."

The upside to it is miniscule: I know I can sell thousands of copies of software for $30, because I've done it, and am reasonably certain that I could sell accounts at a new SAAS for $100 / month, given time to work on it. I am not sanguine about my ability to sell thousands of copies of a book/ebook -- my most loyal blog readers number in the hundreds, if that. I'd also expect massive pushback on the prices that I think make sense -- for examples, take a look at every launch of a non-software info product on HN. (I think I'd be particularly at risk for that because a non-trivial portion of my audience likes the fact that I started a business for $60 -- and when you have $60 in your budget, $X00 on a book is right out.)

There are also psychic costs to me. I kind of value my participation at HN and the Business of Software, for example. It is my sanity-preserving lifeline. I'd really hate to have every post carry the implicit disclaimer "Warning! He is trying to sell you something."