I think that addiction is heavily dependant on the personality of the individual--some people are significantly more inclined toward addiction than others.
I base that notion off of the fact that I've never become addicted to anything (that I'm aware of, at least) so I can't really relate to how it feels to be addicted to anything.
Gaming, for example, is something I very much enjoy, but it's neither the crux of my existence nor something I feel compelled to do. It's something I do because I consider it a great escape from reality and something that excites my imagination.
Also, I feel that most people who accuse gaming, internet, media, etc for "addiction" don't understand the medium to begin with, or the real-life factors that might lead an individual to seek a permanent form of escapism.
The question, "Is gaming an addiction?" is one that dodges far too many complex factors involved in what forms an addiction. However, it could be simplified by saying that while it can be an addiction, in itself it isn't one.