I know that the RON used in the EU and AKI in the U.S. differ, which is why many people think that US fuel is worse due to the lower numbers. But that was not what I was referring to (and I did not write anything about it). I also know of the difference between U.S. BHP and EU PS, which makes up for the difference in figures of 420 PS and 414 BHP, both of which are figments of imagination, BTW:
The engine was developed to put out 400 PS (like the N54, which was the other possible alternative at that time), but when it arrived, Audi already had their 4.2-liter V8 with 420 PS, so that BMW chose the same number. It is a known fact that few S65s actually develop 420 PS (if at all, only with one of the later software updates).
I already quoted the TOP TIER gas initiative, which was formed by BMW, General Motors, Honda, Toyota, Volkswagen and Audi, who "recognize that the current EPA minimum detergent requirements do not go far enough to ensure optimal engine performance", read all about it here
I also cited the numerous N54 high pressure fuel pump failures, which have been mainly observed in the U.S. Matter-of-fact, BMW was forced to raise the warranty timelime for that part to 10 years, but ONLY in the U.S.
And, as a matter-of-fact, these are the coding settings for my EU-spec M3's ECU (MSS60):
As you can see, the value for "KRAFTSTOFFAUSLEGUNG" (which translates to "fuel adaption") is "wert_01", which is for EU. "wert_02" would be for US-spec vehicles, so there has to be a difference.
Thus, I tend to believe that - apart from TOP TIER fuel - U.S. fuel is generally worse than, say, fuel sold in Germany.