NPD also includes consumer side tracking (ie: polling) in their methodology. In fact, that's specifically how they cover Wal-mart and Sam's Club.
Hell, NPD had a registered polling base of 1.8m. They tout it on their site even.
True. By "just"I didn't meant that was all they were doing, I meant that it was the exact same thing. In otherwords that THEY are polling as well.