Many if not most addicts come from some kind of religious tradition. Of course, when the addiction starts to become a noticeable problem, the addict will first turn to religion for the cure. While that is not a bad instinct, it almost never works.
If the 12 Steps rely on spirituality, and religions are about spirituality, then how come the religious exertions of addicts don't work?
Well, it is all about the scale:
You can see here that the scale does not exclude religion. Even an atheist can have a religion, such as Buddhism (http://en.wikipedia.org/wiki/God_in_Buddhism) and Laveyan Satanism (http://en.wikipedia.org/wiki/LaVeyan_Satanism). 'Religion' is one's view of the cosmic order and how one interacts with it. It can have nothing to do with God or gods.
This is why religions can often be abused by people: just as people can have a variety of political opinions, so people can also have a variety of religious opinions. The problem is that the origins of religions comes not from the self, but from someone else: people are not born knowing who Jesus or Siddhartha are, and so they are taught from the experiences of the previous generation.
But, transmitting religious information and transmitting belief are two different processes. Just because you go to Sunday school does not mean you will believe. many people think that by sticking their kids in class every Sunday they will learn their faith. Nope. What they will get is information about it, but they won't necessarily get it.
Addicts may have religious formation, but do they really believe? The answer, upon closer examination, is 'no' and 'yes'. Someone who develops full-blown alcoholism will have a degree of belief: he may have superstitions about God, or very complex intellectual concepts about God (i.e. Gnosticism), but he is certainly not a penitent. He's too scared to take up that burden.
There are addicts who are angry at God. They drink because of their rage at Him, and these are often the easiest people to help because God means something to them. If you see the scale, the antitheist still has a relatively higher level of belief than an agnostic, who must be convinced to get off the fence. the antitheist is over the fence but hates it. As I said before, you can't get angry at something you don't think is real.
But, my point is this: religions can often have a high degree of self-reliance. Buddhism is a classical example. However, there are many forms of Christianity, such as the Amish and Hudderites, who also are very much self-will oriented. A fundamentalist is a person driven by the rules he must fulfill to receive what he wants. If he fails, then God will not help him. This makes him his own primary means of salvation.
Believing there is a God and believing that He will help you even when you cannot help yourself are two different things. See a Creator and seeing a loving Creator who has an interest in you are also two separate categories.
Addicts tend to believe in the former, but not in the latter. But, the former will not save you, and so really what recovery is about is not whether an addict can be made to accept the existence of God, but rather can he accept a certain kind of God.
If you move up the belief chart, you are moving in this direction of a loving God who will help you even when you reject Him. Whereas the further down you go, the less 'god' has any interest in you, to the point that there is the ultimate disinterest of non-existence.
Only a loving God is worth believing in.