What is being said here is that gamers have a neurological structure which makes them more sensitive to the brains own reward mechanism. As any current / former addict will know, this reward mechanism runs on such yummy, yummy chemicals as seritonin, oxytocin and dopamine. The implication being that gamers have more addictive personalities. The researchers are also careful to point out that this implication is only an implication and that they cannot say whether gaming makes someone more susceptible to addiction (can you imagine moral outrage) or whether gaming attracts people who already have a predisposition to addiction.
Now, I personally, being a hardcore gamer, a former drug addict and from what I understand about the remarkable plasticity of the human brain, think that it's probably both. Despite it's seemingly mainstream acceptance I think that we have a long way before gaming will have mainstream cultural legitimacy. I predict another generation or two when all those baby boomers are dead and the people who have grown up with gaming all their lives are retiring.
Gaming addiction isn't even officially recognised in The American Psychiatric Association's current Diagnostic and Statistical Manual of Mental Disorders (DSM-IV.) These people have obviously never even read about the phenomenon of WOW and it's players, let alone met one or (god forbid) played themselves.
P.S. I've never played WOW by the way, I know my weaknesses.