Another possibile explanation for the perception (not for any statistics on performance) is a general shift in the way people drive. "Hypermilers" intentionally drive in ways that are proven to improve fuel efficiency. (Going slower, planning ahead to use the brakes less, etc)
I don't have any evidence to support this, but my own subjective observation is that in general there seem to be a higher percentage of aggressive drivers today than there were ten years ago. There is a lot of evidence[PDF-FuelEconomy.gov] to support the idea that agressive driving has negative effects on fuel efficiency. "Hypomilers"?
At higher speeds, typical of urban expressway driving, however, the fuel economy penalty of aggressive driving is both significant in magnitude and more consistent across all cars. The average car is likely to experience a penalty of 33 percent, with more powerful cars experiencing a somewhat lower penalty of about 28 percent. Hence the impact of agressive driving seems to be especially large at high speeds.