Certainly not all pork butts are created equal, especially if you are talking about portions and not the whole shoulder. I have found that Sam's Club butchers cut some pork differently than most other stores, and it was surprising to me to find they seem to cut the same no matter where the Sam's Club store is. I'm not a butcher but I find that generally there are two very different muscles. My SO calls them the "white meat" and the "dark meat." The former is lean and can be a bit tougher, and the latter is juicier and more tender. Just my observations.