The section you refer to is in the EULA, but it doesn't work like you think.

EULA 3.B
"You may permanently transfer all of your rights and obligations under the License Agreement to another by physically transferring the original media (e.g., the CD-ROM or DVD you purchased), all original packaging, and all Manuals or other documentation distributed with the Game; provided, however, that you permanently delete all copies and installations of the Game in your possession or control, and that the recipient agrees to the terms of this License Agreement."

The key is the term "all of your rights and obligations under..." Now read this:

TOS Section 3
"Notwithstanding anything to the contrary herein, you acknowledge and agree that you shall have no ownership or other property interest in the Account, and you further acknowledge and agree that all rights in and to the Account are and shall forever be owned by and inure to the benefit of Blizzard."

Here Blizz says that you do not own the account. You have no rights in the account. Because you have no rights in the account itself, transferring all your rights as provided in the EULA does not transfer the ability to use the account. Therefore, when you "sell" your account you don't really sell anything at all, and that's why Blizz will give it right back if you ask.

When you purchase WoW you purchase the discs and the right to install the game on your computer. Once you do that, BLizzard allows you to use an account to play on their server. It's easiest to think of your account and access to the Blizz server as a completely separate program that you can rent for $15 a month (Because that's what it really is). If you were renting a couch from Rent-A-Center you could "sell" it to a third party, but they wouldn't actually receive any rights in it. Same idea here.

Looking back that seems long-winded but I think the concept can be hard to understand. I work in software licensing and distribution so I'd like to think the above is fairly accurate.