For something to be addictive, it's got to be able to affect people directly. It's not the *game*, it's the *person*. A compulsive gambler is not addicted to gambling... if it weren't gambling, it could easily be something else that gives the same thrill.
For me, it's word "addictive" in general. A video game cannot be addictive, no mater how fun it is. Addictive means more than just "so much fun I don't want to stop".
They can be. There are people who have died from playing video games, because they are completely unwilling to stop for anything. It has to be people with strong addictive tendencies in the first place, and it's almost always in connection with MMORPG's, but they can be addictive in the true sense of the word.
Something can be habit-forming, but for something to be addictive, there's got to be a chemical reaction that, once the subject is removed, causes a negative biological reaction due to dependency. Video games, gambling, lolcats... they just don't have that ability.
That doesn't make it any less enthralling to the person who's in their grip. But addictive just isn't the right word.
I'm no chemist or doctor but I'll have to argue that video games, gambling and even lolcats, once removed can and will cause a negative biological reaction due to dependency to whichever hormone or chemical playing the game was producing (think adrenaline). Some people get 'high' on the adrenaline boost of gambling millions or skydiving - take that away from them and they do get into withdrawal in the medical sense of the term.
Even running can be addictive, force someone who is used to running 20 Miles every morning for the past year to stay and not run and you will have one big mess of a person (cravings, aches, pains..).
So yes, at first the chemical imbalance was in the person, then was met by whatever activity filled it, so a gambler could focus on skydiving instead, but that's how drugs work too.
Just because general you don't get high from the endorphin by a simple jog doesn't mean someone won't get addicted faster, much like we all have different reactions and thresholds to drugs.