Although this topic has been beaten to death over time, I've always looked at it in the sense that in relation to motor oil, the differentiation of producing variants would almost certainly cost more than the cost savings to WalMart. Generally, the rolling ST oil contracts fill that void and not SOPUS, Valvoline, or Exxon/Mobil going to Bentonville and negotiating an altered product that costs them more to produce.
Apparently, there are certain electronic items, for example, that have specific WM SKUs and are mostly the same but differ in minor ways. I don't think oil companies would acquiesce to that type of variance just due to the nature of the business versus having a separate assembly line for a slightly different chipset or functionality made in numbers that's contracted for WalMart and Sam's Club and/or other mass marketers.
