What are the effects to the end user of that factor?
Because the federal government measures fuel economy in MPG rather than BTU, it is basically encouraging consumers to buy diesel, even though it doesn't really save energy. The E85 fuel has less energy density than gasoline, so the fuel tanks have to be larger to get the same range as earlier gasoline vehicles. Back in the 70's when the CAFE standards were started, diesel powered cars were considerably dirtier than gasoline and didn't have to meet the same emission standards. I'm not sure if late model diesel powered cars today burning low sulfur diesel are as clean as modern computer controlled fuel injected gasoline engined cars.