My Dad is an alcoholic, and I've had issues with drugs and alcohol so I'll give you my 2 cents, for what it's worth. He and I have talked and wondered about this topic quit a bit; mostly about the differences between people and what their real diagnoses are.
He goes to AA an so is of course for total abstinence. I used to party a lot when I was younger, more than average, and I eventually realized that I needed to clean up my act if I was going to live a normal life. So I did--I quit drinking (and drugging, but that was mostly just pot) and finished school, etc. At some point I decided that I really didn't have to or want to continue to abstain completely, and so now I don't. I have to watch how much I drink, because I still like it a lot, but as long as I'm careful and keep track, I'm fine. This is has been many years ago now, quitting in my early twenties and then in my late twenties deciding I didn't have to forego completely. Now, I have periods of time of drinking more or less; I'd like to keep it to less for health reasons.
OK, as far as what is going on with alcoholics--I think that in a lot of cases the alcoholism is just one symptom of a larger mental illness. Anybody who has been around people from AA know that often they have a lot of issues other than just alcohol. (I think my Dad's problems were a combination of a terrible childhood, extreme anxiety, and an OCD-like condition), and just as people with any mental or physical illness can do things that make the disease better or worse, they make their disease worse by drinking. On the other hand, Dad says that there are people in AA who once they quit drinking are pretty much "cured", meaning that they have no residual mental health issues--their problem was purely due to their drinking. Did I have some other mental issues that caused me to drink? I don't know for sure, but I don't really think so; it was just the time and place and crowd I chose to hang out with; wanting to have fun. I don't have much going on now mental-health wise except for the nagging things I put in my intro post; things I'd like to take control of better in my life.
So--I think there are people who have a "disease" (some sort of mental condition) which includes problem drinking, which exacerbates the original problem. Other people, for whatever personality reason, just like to drink and sometimes drink to excess, and this can become a habit, but if they break the addiction, they will be OK as long as they are careful and remember their propensity. Then it becomes like any other sort of tendency that you know about yourself and have to watch out for (bad temper, over-eating, whatever indiscretions a person may be prone to.)
This is all purely subjective and personal, but there is no reason to think that I am the only person who ever drank too much and then was able to quit and then go back to drinking fairly responsibly. I really d0 think it depends on what else is going on with the person's mental state.