Actually, the octane rating overseas is just different rating system, honestly. 100 octane RON (Researched Octane Number) is actually aproximatly 95 octane, at most. 98 RON is most common for premium in Japan, which equates to 94 octane PON (Pump Octane Number). PON is derrived from MON+RON/2=PON. MON is motor octane number. The variance in foreign fuels is typically higher, so it can be up to 2 ratings of difference, which equates 98 octane overseas to aproximatly 92-96 octane here, the same as the premium we get on the East Coast. If you take a look at Sunoco 93 octane tests (which I can't find the link to right now x.x), they typically actually test to 95 PON, which is better than most. Mobil ranged right around 94, Chevron's 91 about 93, and so on. So, we get comparible gas here. =) Tuning is just a matter of emissions standards, safety/crash standards, and acceptible environmental performance variance, typically. Since the climate and elevation in the Yoo Ess of Aaye varies SO much between state to state, and so on, the ECU's have to be 'sloppily tuned' to function under a variety of conditions. Bumper regulations for foam thickness, density, crash resiliance and rebound also have to be passed upon import, and so on.
It also doesn't help that your average American wants a car that gets him back and forth to work without spilling his coffee, and with minimal thought involved in the driving process, we get slower, less 'edgy' cars here. It's all a matter of supply and demand; If people demand a luxoyacht out of even the most economical of cars, suddenly the demographic turns that way, and luxury options become standard, and performance options become depricated, despite what the lower portions of the demographic have to say.
Ahh, well. =)