It was highly pirated, so i bet sales are pretty big too, everyone was waiting blu-ray version for so long, besides, both versions(2D 2.35:1 and 3D 1.78:1(open matte)) are on 2 blu-rays, so quality is overwelming(google - http://www.blu-ray.com/news/?id=9541), it's a must buy, like BttF, SW or LotR.
It's a pity there is no way to track sales at least like videogames(vgchartz), even thought digital probably takes the majority.