This is the only thing i have found where anyone mentions the sandbenders, and I was wondering if I was the only one who thought maybe the sandbenders were actually what's left of the airbenders in hiding. I think of it like this - if they can't bend other earth than sand, maybe they are really bending the air and the sand is being blown around with it, but everyone thinks it is a form of earthbending. They would do this because for a hundred years no one knew where the avatar was, so my guess is that after the temples were wiped out, any rumors of airbenders still practicing would have been hunted down...