55 wasn't about safe it was about saving fuel.Are there a lot of non synthetic A5/B5 rated oils? My point is that if you're running an oil with that rating, then it's not an oil quality or economics issue. Mexico may tend to be warmer on average, but 0 degrees C in Mexico is the same as 0 degrees C in the US.
I'd believe the US recommendations more if they varied over the temperature range or use case, allowing for the fact that not all operating conditions are the same. Instead they say 0W-20 and nothing else, in all temperatures, in all applications, all the time, no matter what.
These CAFE oil requirements feel like the old 55 mph national speed limit. Yes, trained engineers did studies on the freeways they'd built, applying scientific principles to determine the optimum travel speeds with which to set speed limits. Then politicians came in and threw out the studies. They replaced it with "55 sounds safe, so you can never, ever, under any circumstances go faster than that."
The world is too varied and too complex to be regulated by these kinds of one size fits all policies.