I think what’s happening, not just here in the United States but in other countries as well, is that there’s some percentage of gamers — and no one quite knows what the percentage is, different surveys have put it at different percentages — but for some percentage of gamers, it seems to become an obsession. Other things in their life get neglected, sometimes even their health gets neglected, their grades start to suffer, relationships start to suffer, and so it starts to bear all the behavioral hallmarks of an addition. And so I think that’s why the term has emerged. Of course, the term itself is controversial, because there are some, particularly in academia, who say that addiction signifies something that has to do with a chemical change. A dependency to a chemical. But we do have other behaviors that are recognized as addictions, the most common example to bear would be gambling addiction. - Dr. David Walsh of the National Institute on Media and the Family

Game addiction seems to be a hot topic lately. This might be one of the big study trends in 2009. I think games have addictive properties, just like anything else out there. It's the people that get addicted to them that need to be studied, not the games in particular.

Full interview here