Where have all the spambots gone?

As an update to the WoW gold spamming story I wrote earlier, I have noticed that in the last month the spambots have gone. There is still some spam, but I could swear that SpamMeNot has been reporting less and less spam recently. I have also noticed that the corpses have gone from Stormwind's Auction House.

I have been searching official forums for an explanation, but so far I have found none. It is interesting that forum moderators are ordered to delete spam-related threads immediately, so I have not found any mention of this. I can only see one of these options as the reason for the reduction of in-game spam:

• Spammers have given up after the many thousands of deaths, and moved somewhere else (unlikely).
• Gold websites have disappeared (even unlikelier).
  
• Blizzard has recognised this as a serious problem, and have implemented a technical solution that gets rid of most of the problem.
  

I vote for option 3, but I do not know how this has been achieved.