I don't know what's worse: your complete disregard for the fact that there are many people out there whose brains are simply wired to be prone to addiction, or the fact that you acknowledge that in your first sentence and then promptly write it off in the second. I'm sorry, I don't mean to be a prick, but it's not that simple.
You can become addicted to anything that gives you pleasure (it isn't that simple, but for the sake of argument). Booze, drugs, sex, gambling, more. Addiction has very little to do with someone's will, and more to do with the chemicals the brain releases when the addict is involved with thier vice. Sure, it takes a strong will to break the addiction, but when one becomes addicted in the first place, they often don't even realize it, and aren't prepared to break that addiction. In short, the will has to be built up, through therapy, treatment, and from within. Many strong-willed people aren't strong enough to deal with addiction, at first.
Now, if you get clean, and then fall off the wagon...while it's understandable to a point, that may be the result of a weak will (or it may be outside factors). However, it's still hard for anyone to judge, since addiction is often a life-long disease that people never fully beat.
And yes, there are addicts and former addicts in my family, so it does hit a nerve, and I do know what I'm talking about.