Of course it is. I have said the same thing in this forum many times in the past few months. (Some people get real angry about it, too, seemingly insisting it's not within their control.)
But, since you mentioned alleged "improvements in mpg" since 1981—something which is also within their control—I just thought I'd mention the kink in your comparison.
I think it was Patrick Bedard a few months ago in Car And Driver who compared today's gas mileage to that of a decade or two ago and found that it's going down, not up, due to higher vehicle weights and consumer choice.
It is not alleged, but certainly smaller than I expected when you look at volume averaged figures that take into account increased market share of light trucks and other lower mpg vehicles. 23.1 in 1980 and 25.2 in 2005.
SUMMARY OF FUEL ECONOMY PERFORMANCE, MARCH 2005, U.S. DEPARTMENT OF TRANSPORTATION, page 4