My cofounders and I developed Softcover [1] to support the business model used by the Ruby on Rails Tutorial [2], which combines "tech cred" with a profitable product business. I plan to reveal more detailed numbers soon, but I can say that the Rails Tutorial has made an order of magnitude more money than the "solid success" benchmark mentioned in the OP, despite (or perhaps because of) making the book available for free online. (I include revenues from screencasts, which are a lot of work to produce, but are much less work than initially writing the book.) Thus, with a platform like Softcover, authors don't have to choose between making money and building their brand.
[1]: http://www.softcover.io/
[2]: http://www.railstutorial.org/, but watch http://news.railstutorial.org/ for an announcement of 3rd edition draft chapters, which I plan to start releasing shortly