Announced on the forums:
We’d also like to take this opportunity to thank the community for their assistance in reporting suspicious behavior. Numerous account closures come as the direct result of tips reported to our GMs in-game or emailed to firstname.lastname@example.org.
We appreciate your support and wish you the best with your continued adventures in Azeroth!
Observation #1: Wow… That’s more than what most other mmorpgs have in TOTAL subscriptions.
Observation #2: Blizzard is crazy? No. They are just making the game a better place for all the other players who respect the rules. That’s “quality” as well. It is also important to not legitimate what goldsellers do.
Observation #3: Uhm, is this really a news as big as it appears? The announce says nothing about WHERE those accounts were banned. In USA? In Europe? In China? Everywhere? I cannot remember right now, but isn’t creating new accounts in China really cheap? Without those details we cannot know the real consistence of that announce. Even if I guess it’s just the USA (the announce wasn’t copied on the european forums, for example). In that case it would be around 4% of total subscribers.
Anyway, the goldsellers and bans are still only consequences of a problem. That problem is still a design problem that is waiting to be addressed.