But the actual complaint ( http://docs.justia.com/cases/federal/district-courts/new-yor... ) suggests that the publishers allege much more. You don't have to agree with the publisher's claims (you obviously don't), but be fair and give the full picture.
The publishers claim that Boundless is copying the chapter titles, subtitles, subheadings, and pagination of each book, using pictures of the book as marketing materials, and then paraphrasing 100% of the text of each book.
It's true that you can't copyright facts, but paraphrasing on such a fine level is often considered copyright infringement. Even Wikipedia forbids close paraphrasing unless the original material is in the public domain or there is absolutely no other way to express it: http://en.wikipedia.org/wiki/Wikipedia:Close_paraphrasing
Universities also consider close paraphrasing to be plagiarism: http://library.csusm.edu/plagiarism/howtoavoid/how_avoid_par...
And a court 100-ish years ago found that a close copy of an economics textbook was a form of copyright infringement, in a very similar pre-digital case (it's not like the digital era is the first time that people have noticed that books are expensive):http://en.wikipedia.org/wiki/Macmillan_Co._v._King
Should that doctrine apply here? Is it a good doctrine in the digital era? There's room for debate. But you'd never know that from the blog post.