I think with trying to quit any habit, there's a certain amount of physical dependence, but it can often be overcome with the right amount of mental discipline. Not to discount the physical needs, but I think without the mental, you aren't going to overcome anything. And I think it's often the will that is weak. The commitment just isn't there. Habits die hard and I think that for lots of people it's a matter of not wanting to suffer for any goal. Certain things can jar your mind to become focused on your goals. Sometimes it's a heart-attack and the doctor tells you to stop - that fear of death. For some women, it's pregnancy. In the JWs case, it's the fear of God and disfellowshipping. It's just that extra something to help you stay focused. Sometimes that's all that's needed to boost a struggling will.
I still don't think it's any easier for a JW to give up an addiction, but they do have the advantage of having a will dedicated to quitting.
My dad quit before he had even started up with the JWs. One day he and his brother asked themselves what they were doing smoking, because they knew it wasn't good for them and was considered a bad habit (and we're talking way back in the 1940's). They tossed their packs in the gutter and quit right then and there.
I've tried it from time to time. Smoke a pack, quit for a month or two, smoke another pack, etc. Haven't had a cigarette in over 5 years now though (only an occasional cigar). I think some people just never get the physical addiction, which makes it easier to quit.
