It is true that they do make different models and/or model numbers for the "mass merchants" (e.g. Wal-Mart, Costco, etc) and the "specialty" sellers (e.g. Best Buy, HH Gregg, etc.)

I found this out this past Christmas when we finally decided to get a big LCD HDTV. We wanted a Sony, and found that there was a 95 dollar difference between the "speciality" store and the "mass merchant." "Speciality" store model number ended in "500" and mass merchant model was "501" Careful comparison revealed no difference in specs between the two. However, the different model number did allow the "speciality" seller to avoid having to "beat any competitors price" under their advertised policy because "they are two different models."

So I bought the cheaper mass merchant version and saved the money.

There is no general rule as to what the differences are. I have found some brand name things sold by Wal-mart and Costco to seem to have been "dumbed down" to meet a lower price point.