You could easily write a whole book on creating a CMS, I think the chapter covered the basics enough to let people use a bit of logic to work out how they could expand on it themselves if they wanted to.

It gives a good grounding for the basics. If people can think logically then they can usually advance a lot further after reading the book. Of course the security aspect should come in next which is when I would recommend the Php|architect’s Guide to PHP Security.