While it is true they don’t ban for AH related or general sales related things, there IS an economy related Ban category. It is used for RMT related offenses.
Example of the email a player would get for that category.
Account Action: Account Closure
Offense: Exploitative Activity: Abuse of the EconomyThis account was closed because it was involved, either directly or indirectly, with the unauthorized exchange of in-game property for “real-world” currency. This exchange detracts from the integrity of the World of Warcraft game environment.
The account holder is responsible for all activity on the account. We issue suspensions and closures to protect our players and our service in accordance with our Blizzard EULA
We don’t take this decision lightly. Our team issued this closure only after a careful review of relevant evidence. Our support staff will not overturn these closures and may not respond to appeals. For information, see our article:
In some cases, these actions happen when a third party compromises an account to sell gold or other in-game property. If you believe your account was compromised, please follow these important instructions:
Regards,
Customer Service
Blizzard Entertainment