The problem here is that people are confusing the nature of the fix with the cause of the addiction.
The boy clearly has some issues that are bigger than a gaming addiction - I mean, seriously, if you absolutely have to steal a girl's earrings to get money to play an MMO - why beat her to death with a rock to do it? She was SEVEN. I'm pretty sure a 15 year old could have intimidated her into handing them over (still horrible, but at least she'd be alive). Beating someone to death with a rock for a pair of earrings is the sign of a disturbed mind to begin with. The game is incidental - he might just as easily be addicted to crack, or alcohol, or coffee for god's sake, and would still kill someone to get a fix.
I can't speak to whether games are clinically addictive, because frankly, no-one seems to be able to prove it one way or another. I do think that people should keep perspective here though - kid beat another kid to death for her earrings. A gaming addiction is not the main problem here.