Here's that video from yesterday I mentioned that you should check out. It's called "Unethical Game Design", and it's a pretty good watch whether you apply it to WOW or Diablo 3.
Even Activision and Blizzard have teams of psychologists working for them that perfect methods of behavioral addiction in video games and encourage compulsive behavior. They try to avoid the label "Psychologist" though, often they're grouped into "Marketing & Promotion", "Business Intelligence", or "Statistics and Data Analytics". Internal Psychologists for employees are rare, but they would probably be grouped under "Human Resources" since they would be providing services for employees, rather than analyzing customers.
(Most large game companies do this by the way.)
You can use some of my earlier search methods to find these employees yourself if you want. For example, you'll find employees doing jobs called "Data Visualization Analysis", "Business Intelligence", "Localization Analyst" or "Statistics Analysis" and yet they don't have mathematics or business backgrounds.. but they do have Masters and Ph.D's in behavioral psychology, community/organizational psychology, consumer psychology, and experimental psychology.
They're like the fabled "Fraud Manager" positions (which were renamed to "Finance Services" or something else to cover their purpose). They don't exist. ;)
One day, Achievements won't be enough in Call of Duty and they'll need to come up with new ways to keep players addicted. (Blizzard is introducing "Pokemon" Pets for example.)