Why does the author believe introductory Computer Science textbooks provide poor value?

"I’ve been teaching Computer Science since 2008 and was a Teaching Assistant long before that. Before that I was a student. During that entire time I’ve been continually disappointed in the value (note, not quality) of textbooks, particularly Computer Science textbooks and especially introductory textbooks. Of primary concern are the costs, which have far outstripped inflation over the last decade while not providing any real additional value. New editions with trivial changes are released on a regular basis in an attempt to nullify the used book market. Publishers engage in questionable business practices and unfortunately many institutions are complicit in this process. In established fields such as mathematics and physics, new textbooks are especially questionable as the material and topics don’t undergo many changes. However, in Computer Science, new languages and technologies are created and change at breakneck speeds. Faculty and students are regularly trying to give away stacks of textbooks (“Learn Java 4!,” “Introduction to Cold Fusion,” etc.) that are only a few years old and yet are completely obsolete and worthless. The problem is that such books have built-in obsolescence by focusing too much on technological specifics and not enough on concepts. There are dozens of introductory textbooks for Computer Science; add in the fact that there are multiple languages and many gimmicks (“Learn Multimedia Java,” “Gaming with JavaScript,” “Build a Robot with C!”), it is a publisher’s paradise: hundreds of variations, a growing market, and customers with few alternatives."