Our squadron superintendent took 2 weeks leave to play World of Warcraft when the expansion pack came out....yea, and this guy gives me orders. He fits the stereotype. Short, nerdy, thick glasses, obnoxious - This is what nerds really grow up to be - a nerdy boss.

We have an airman that plays as well. Shes 24, pale as a ghost, has a haircut straight from 1945, thick glasses and is probably the nerdiest/oddest girl Ive ever met. Always talking about her level and characters and server...

"Sure, over 8 million people play WOW - but 6 BILLION people play REAL LIFE"

 

Like other people have said, there seem to be people who are more prone to be involved with addictive behaviour. I think it's possible to be addicted to anything. It wasn't that long ago that most people thought gambling and sex couldn't be addictions. If the behaviour results in negative consequences, there's obviously potential for problems.
While I have issues with the DSM, I think it will be interesting to see if the AMA makes distinctions between adults and children (as they do with other diagnoses).