Originally Posted by floydarogers
It isn't politics so much as need: most of the US isn't cold enough to require higher cetane to help while starting. And after the engine is started, cetane appears to have little or no effect on mileage or power.
Which would explain why most of the "premium diesel" is located in the northern tier states. But it does not explain why the party line for BMW is to run 51 cetane or higher.