The book focuses on the 20% you need 80% of the time. The pages saved are used to introduce you to the Hibernate "ecosystem": how Hibernate can work with other common development tools and frameworks like XDoclet, Struts, Webwork, Spring, and Tapestry.
The book builds its code examples incrementally, introducing new concepts as it goes. It covers Hibernate's many, useful configuration and design options, breaking a complex subject into digestible pieces. With a gradual "crawl-walk-run" approach, the book teaches you what Hibernate is, what it can do, and how you can work with it effectively.