What I have found is a different quality of rib, even though it may come from the same plant.
The ribs at Costco, packaged in cryovac will be meatier and more dense than the same package of Hormel that I find in the grocery store. They also will be smaller per rack as opposed to the ones found at Costco.
I do believe there are different grades possibly packaged for different retail institutions. I don't know, not familiar with the practices of retail distribution.
There is a fluctuation of price at the warehouse stores depending on the season by about $.30 per pound.