The Amazon description is not the best description that should be there. It was a quickie write-up by the publisher early on. Still need to get it corrected.
A better description is available on my blog here :
http://pronetbeans.com/archives/6 If you want a book that strictly deals with NetBeans Plugin development, see Rich Client Programming: Plugging into the NetBeans(TM) Platform, by Tim Boudreau, Jaroslav Tulach, and Geertjan Wielenga. Otherwise I will obviously recommend my Pro NetBeans
IDE 6 book.