I agree with you, Barry.
The book is just one more aid to achieve the certification.
I had 2 questions in my exam that I didn't learned from the book but also from other sources of study.
One question about Collections had methods from List and Iterator, which both I thought it wouldn't appear on the exam so I didn't bother to study. But, as the answer had multiple choice, I could eliminate the ones I was sure it was wrong...
Another one about threads had daemons, and this I studied from the Heller's book.
So, my advice is the same as yours: don't study from just the book.
Take many mock exams, see the JLS, and, of course, come to javaranch to get answers and to learn more and more!