Be aware that per the per the Preface to the Third Edition on page 15, and as visually indicated by the change in the color of the headings and footings on each page, chapter 12 is not quite ready yet. Rest assured that the text and the code will be brought in sync in a subsequent beta. :-)
I’m new to this whole “beta books” concept and have found out that despite all the warnings and visual clues, I’ve received plenty of errata concerning parts of the book which aren’t ready yet. And such issues are often not reported just once, there are plenty of dupes.
What you are reading in that chapter reflects my folding in fixes for a number of reported errata, as well as my initial testing of the downloadable code. I would have prioritized completing that chapter higher except for the fact that Rails 2.1 came out and that seemed more urgent.
My purpose in pointing it out was not to chastise (far from it!), but in the hopes of preventing further surprises and possibly even future disappointment. Anything reported (particularly via the errata system) will be investigated and resolved.