Yes, the JBoss folks were pretty helpful. Norman Richards was a solid tech reviewer and was very supportive. JBoss listed our book on their web site to help market the book, too.
We wrote the book because we felt that most of the books and documentation were useless to developers. The other material is good reference, and shows the internals and architecture of JBoss.
But since J2EE is a specification, then your code should be portable across application servers. As a developer, you really don't need to know the internals/architecture of the server. It just needs to work well and conform to the J2EE specification.
So, we wrote the book because there was a lack of good developer documentation, and we wanted to show examples of how to deploy the most commonly used J2EE technologies.