A dispiriting story. The comments to David Flanagan's post are interesting, for a taste of the debate similar to those some of the comments to your posts have provided David. See "Charles", especially.
The textbook market is particularly threatened, I think. Textbooks can be extremely time-consuming to write and are usually (unlike Flanagan's) created in the spare-time of teachers and lecturers; the market is currently dominated by some very large publishers. I can't think of a financial reason why anyone would want to write a textbook today, unless they have a strong pre-existing brand. Somehow or another authors have to find ways of making their earning capacity less pirate-vulnerable. Current remedies, such as they are, self-evidently aren't working.