Yeah, but a lot of the time the codependency doesn't have to do with the alcoholic/addict wanting to "take advantage" of anybody. It just kind of happens because you love them and you don't want to see them distressed, so you "help" them in the short term and end up hurting them and yourself in the long term. It's poor judgment on both peoples' parts. I just don't think that an addiction would turn you into a person who is willing to coldly manipulate others for your own benefit--not unless you were the sort of person who would have done that to get out of a tough spot even without the addiction.
But then, I've never had an addiction, unless you count self-injury (which I do, marginally, but still isn't quite the same thing). Maybe it really does change you into a manipulative, nasty person. But until I have evidence to the contrary, I tend toward the belief that it does not.