For WOW, according to the manifesto, it's used as cover. The original word says that "using social taboos is an extremely effective method from preventing people who know you well from digging too much." The taboo Breivik mentions is WOW, as he says "F[or] example, tell them that you have started to play World of Warcraft or any other online MMO game and that you wish to focus on this for the next months/year."
As the article says, video games are used in crime, who should be blamed?