Daniel555 - that is the only question the elders care about, and the standard question they will ask when anyone has doubts. They don't really care if you don't believe some doctrine, as every elder disagrees with things, shelves questions, and waits for new light. But if you do not believe the Watchtower represents God's slave class, then you are an apostate and a danger to the congregation.
What I found strange in my paperwork was that non-belief in the Bible is not a matter for being disfellowshipped. See http://jwfacts.com/images/1-2005-CO-report-marked-s-303-form.gif They were only concerned if I was to tell others. When I had my judicial committee, though I had told them I did not believe the Bible, they still kept asking me if I believed the Watchtower represented the Slave. That really is what makes a person a Jehovah's Witness. I think there is a lot more fear of a person that claims not to believe in the Slave, than someone that claims not to believe in God or the Bible, because they are more of a threat to the congregation, because it indicates they have information that is a lot more damaging to a person's faith.