Why my mpg does not match promised values?

Why is it a stretch? With more horsepower, many more drivers are accelerating harder with that right foot than they could back then. I have seen many complaints here about specific cars, Prius included, having 0-60 times that are 'dangerously slow' by the standards of many of today's drivers, even though those cars are actually more spirited that typical econo-cars of the 1980s. I.e. accelerations that were perfectly normal back then, because most cars simply could not do better, are now often (mis)labeled as 'dangerously slow'. Peoples personal standards, and even their expectations (and demands) for other traffic, have changed.

This behavioral shift drags down real-world MPG, thus widening the gap between 'real-world' and the CAFE/EPA ratings still measured at the old slower accelerations.

 

Dueling cats update! Pretty consistently 4.2 ish fat on the MPG display.