Hi Darin,
I wonder if the regulation included FE numbers from the
FuelEconomy.gov web site, which are actual, self-reported fuel use, that this would do several things: the car companies would get credit for what people were actually doing, and it would be a real world incentive for them to encourage people to actually get good mileage?
For example, my car is a 2005 Scion xA with manual 5-speed: the EPA (2007) ratings for this model are : 27/34/30. There are six people reporting an average of 36.4mpg -- this has to be considered a "combined" number, so Scion/Toyota would get credit for 36+ rather than 30mpg. (By the way, my lifetime average for 226 tankfuls is now above 40mpg!)