i think jon has outgrow bob rock and in the future if he changes shanks(hopefully) he will try someone different. we have to remember that these guys know how to make records, they have numerous releases under their belt, and after 3 records with bob rock they know more or less what they gonna get...apart from all this jon is a guy of habbit, he wanted to make these days with him as well if i m not mistaken but bob rock was fully interested in metallica...