Meanwhile, I'm merely saying that it wouldn't surprise me if such a policy exists, whether formally or informally. The distinct lack of any product on Walmart shelves which has a below-RRP price printed on its packaging is strong circumstantial evidence at the very least.

The fact that you mentioned is an extremely weak evidence in the light of very thin margins Walmart has (under 3%), which is more than 10 times less than the old store tax, with probably even smaller incentive to combat.