For most programmers Java 6 didn't introduce much important new stuff. For the purposes of the book, you should be able to use Java 5 and Java 6 interchangeably. I'm not saying that something minor won't come up, but on the other hand I wouldn't be surprised if everything from the book worked the same. I'm pretty sure that we're not going to worry about updating the book until Java 7 comes along.
Spot false dilemmas now, ask me how!
(If you're not on the edge, you're taking up too much room.)