Isn't this based on just 9 months, or something like that?
To be fair to WoW, if that 9 months was actually 12, WoW would have more copies sold. And to be quite honest, I'd be shocked if GW2 didn't sell more copies that WoW did almost 10 years ago. The market is saturated with players now as opposed to in 2004.
But in the end, this is just marketing and it's working quite well considering how many things I've seen about this now.
ANet have a successful MMO on their hands. Nobody can deny that. Good luck to them, I say.