Originally Posted By: HTSS_TR
Oil temperature is speed related, oil temperature rise with speed. In Europe, especially in Germany, a car can be driven at much higher speed than in North America, therefore oil grade is needed to be thicker to be able to withstand oil temperature north of 140-150C. Here we drive mostly 75-85 MPH, oil temperature is mostly around 100-110C or lower, therefore lighter weight is okay.
Here's a chart prepared by Honda in their research which reinforces your point.
US Vehicle utilisation is very predictable, and on the law of averages, they can specify something that will likely be suitable to the vast majority of users.
Unfortunately, US consumers don't like being told that, and therefore assume that their single grade is "optimal", and everyone else is wrong, or hasn't caught up with the Ox carts yet.
Other places, their utilisation is more diverse, so the law of averages means that you need to pick something that suits an extreme(r) end.