I don't think that's necessarily the case, at least not in areas where lots of stations offer the option. Most of our Kwik Trips have E0 91 (labeled as "premium recreational gasoline" or similar) that's marked as top tier on the pump. And I got gas at a BP today that had Amoco Ultimate E0 91, which is top tier. My guess is that top tier stations will have top tier appropriate additive concentrations in their E0 as well, and that non-top tier stations selling E0 (like Maverik, Casey's, Kum and Go, etc.) will have EPA-minimum concentrations of additives in all grades. (But I have seen a few, say, Shell stations that offer E0 marked on the pump as "Not a Shell Product" but that's relatively uncommon, in my experience. Most pumps I've seen don't make any such distinction.)