As expected, you failed to actually read it. Your right to return a purchase only applies to tangible goods in their original wrapping (a physical item you bought in for example a store or had shipped to your house).
For very good reasons, you can't return digital pets or mounts from the Blizzard store already added to your account in the same way that you can return a boxed video game. Common sense would dictate that, and unfortunately for you, it was also included in the terms of sale to which you agreed when you made your transaction. What if I had not been happy with my Cataclysm digital pre-order? I don't suppose I could just cancel my payment and without further ado, the matter would be settled.
Even if you were able to return pets from the store, how exactly would you expect them to go about it? They see that someone cancels their payment without any additional notice; are they then expected to predict that you didn't like the pet and assign an employee to manually remove the pet from your characters?
srsly bliz lol