Right, the idea would be to preserve content in book form when hired to do so by the author. If they wanted to turn around and sell to the public that would be

Right, the idea would be to preserve content in book form when hired to do so by the author. If they wanted to turn around and sell to the public that would be up to them, or they can just print copies for themselves/family/whatever. I’m not familiar with Spolsky’s book, but I am familiar with the contributors and even know a couple. I tried looking through what was available in the "Look Inside" feature on Amazon, but I could not find any info on whether he obtained permission to reproduce those texts. In general I would be shocked if such a well known person did so without permission from so many high-profile authors. Of course, some of the blog posts may have been permissively licensed to begin with (CC-BY, e.g.) but I know not all of them were.