I'm in the US on holidays at the moment, noticed a lot of your pump fuel is 87,89 and 91 octane. In australia we can get 98 octane at the pump and even 100 octane at limited stations which sure helps with running a bit more comp in our street cars.
It's entirely because of the method used to calculate the octane. In the U.S., we use the ((R+M) /2) average, which sits about 5-10 octane lower than the standard RON measurement Europe uses.