What else would they buy it for? There is no extra controller or another game moving the bundle. If they just wanted a ps3 they could buy the 160gb version for $250 and use that $50 difference to buy a game they actually want. I guess maybe they just wanted to save $10 and get all that extra HD space that they wont use?
If by under selling you mean its sales are projecting ahead of any game in the franchise then, yup.