Let me state as a non-smoker myself that I'm not entirely certain that "all smokers don't WANT to smoke". Many I know started because "it was cool"-don't get me started on this one. Nicotine plays a strong role, but it's not the only one, simply because not everyone responds to addictive substances in the same way. I've known a handful of people that just quit and didn't seem at all bothered by any cravings. A minority, to be sure. Other smokers that I've talked to like to have something in their hands, or appreciate the social aspect of smoking. And there's a small handful that actually like the smell and taste. Yes, their tastebuds have been numbed, but that doesn't discount smoking as an aquired taste.
I have a friend who has quit twice before when she became pregnant and then started again sometime after weaning the child. For her, it seems that the social aspect(a lot of her friends and family members smoke) has the strongest affect on her. She's now smokefree while pregnant with her third and I fully expect her to take it up again, at least once in a while.
I've labored over this comment(easy to tell, huh?) because I believe that the reasons people smoke are many and complicated. Nicotine addiction is a strong component, obviously, but I'm convinced that some people would smoke anyway.
Just my opinion. I could be wrong.