I meant to write about this article when I first read it, but Are Games Addictive? The State of the Science at Gamasutra asks if games are addictive. The answer: We don’t actually know.
The article presents an overview of psychology to help a game developer understand the nature of addiction and how it relates to games. Interestingly enough, even though there have been documented cases of people dying while playing online games, there hasn’t been enough definitive research to say whether or not games are addictive. People can become addicted to games, but no one has proven or disproven that games are themselves addictive. It’s a distinction that politicians and journalists have ignored.