I don't have a lot of knowledge of oils, but living in the heart of Wal Mart country with family members working for Wal Mart vendors, I would not doubt for one minute that the oil you get at Wally world could be of lower quality than the same labeled product elsewhere.
It works like this. When you get a contract to sell to Walmart, they have the right in the contract that you must provide the product for a decreasing amount of money. So every year you must sell them the product for less than you did the year before. Wal mart has the right to audit your books to find ways to cut costs.At first this benifits the producer, as it requires them to become more efficient. But eventually there is nothing left to cut, and you either go overseas for cheap labor, or go under. Wal Mart plays serious hardball.
If interested read up on what happened to Levi Strauss, Vlassic Pickle and others.
This is not intended as a political statement, or meant to start any flames. I think the truth is that Walmart vendors are under incredible pressure to cut costs, and if the product quality suffered I would not at all be surprised, and as consumers we should be careful.