Wicht
Hero
I'm not sure that supports your point; my experience with Books-a-Million is that they get their D&D product when someone sells it off at rock-bottom prices because it isn't moving - in many cases that someone is WoTC. If they've got a lot of something than it generally means it wasn't selling through other channels.
I think you are thinking of Half-price books. Books-a-Million is in the same vein as Barnes&Nobles and Waldenbooks. Ours also carries Paizo, Green Ronin, etc.