I actually have a freind who has been diagnosed with clinical depression. One of his symtoms was basically an addiction to Final Fantasy Online.

He would play it till he couldnt stay awake anymore then sleep till he woke up to get back on FF. He abandoned everything else in his life and even lost a huge amount of weight (he was already a thin person to begin with).

This wasnt exactly an addiction to video games...persay...more like the addiction was a symyom of the depression.

Anyway, i would be inclined to believe that depression or some other psycological disorder is more likely to be the culprit in "video game addiction"
And addiction being only when you do the action to the point where it affects your life adversely and are unable to stop.