Um...I must be missing something because noone else said it... but the way they calculate octane where you live is different.
Heck the way they calculate octane between gas companies is different. When they test gas for an octane ratings they test it two way, they test it in a lab to see what the "anti knock" rating is, then they test what the rating is in an actual engine, and they average the two together to get the octane rating that you see on the pump. thats why some place have "good gas" and some have "bad gas" one may have gotten a higher rating in an engine but lower in lab test, some may have gotten higher in a lab test but lower in an engine..but the two still may average out the same..plus different states all have different emissions laws on what additives they can add to gas..
FYI they also have different blends of gas between summer and winter..