while there are *clearly* genetic/biological factors that affect this - for instance, a beer may be 20X as satisfying to you as to me, or perhaps one's ability to find joy in *anything* traditional is so low that drugs truly are their best chance at a shred of happiness - I think that addiction says a ton about the 'mental state' of the individual within the confines of that person's psyche. ((there's also something to be said for the psychological rewiring that an addict experiences, and its effects on continuing consumption, but that still comes down to basic reinforcement in the end)).
I have a feeling I'm completely bastardizing the point I'm 'trying to make, so I'll phrase it like this - the correlation between "life sucks" and "addiction" is huge, and while the two clearly feed off of each other to a large degree, that duality is the root of addiction IMO. I know non-addicts who are "temporary addicts" when "life's fucking them over". Most any addict I know uses LESS when life is going good for them, and they almost always use more when life's going poorly.
A fantastic study wrt this topic is "Rat Park", I wish the study got more attn than it did but there's a wiki page for it. In essence, they had a dual-setup for the whole "rats self-administering drugs", one setup was real nice and a great lil home for the rats, and contained both drug-laced and pure liquids. Those rats chose the pure liquids, not the drugs. The other setups were the stereotypical cages where the rat's in a shithole, and can choose either liquid. These rats chose the drug-laced liquids. HOWEVER, once the rats from the shitty-setups were introduced into rat-park (the nice setup), they did NOT continue to seek the drug-laced water that was right there, freely available to them, instead they drank water and went for a "healthy" life in a normal setup. IIRC, some/many even exhibited w/d symptomology(sp? my spell-check's hitting that but fuckin mac isn't offering an alternative..meh), but despite that they still drank the 'pure' solution.
I think this speaks volumes about both individuals' circumstances affecting their "addictive personalities", and of the larger picture of comparisons between "good, productive societies" and "downtrodden ghetto's". Guess it boils down to "addictive personalities" tend to go hand-in-hand with shitty lives/circumstances. From personal experiences and observations, this holds true almost 100% ;P