The reason the big soda brands use HFCS in the US is because it's cheaper (due to corn subsidies). The speciality sodas like Boylan's, etc. compete on quality, not price, so they are able to transfer that cost to the consumer. The consumer with more disposable income wants to justify the extra cost to themselves and peers. "Oh, yeah, this is 'Mexican Coke'. Sure it's more expensive but it has REAL sugar."
Would the average consumer in the midwest be willing to pay more for a 12-pak of Coke if it had real sugar? Maybe, maybe not.