That's bullshit. Out west where there's literally fucking nothing (or even in West Virgina where it's full of hill and the roads are complete garbage) they put the limit up at 85MPH (140km/hr ish) and so all these huge trucks and wiggle wagons and everything are blasting around close to 100MPH (160km/hr ish) on little two lane roads in the middle of nowhere.
It's pretty nuts if you've ever piloted some huge thing blowing by a truck like a foot away with a differential speed and all the wind of close to 300km/hr. You pretty much just have to hope and pray the other guy has taken enough trucker pills and isn't getting blown off and nobody's tires are about to explode. And then do that all day long.
I think the Australians have the right idea with that madness road through the middle of the desert.