How fast do you drive on all that highway driving? If you're like most drivers, and driving 80-90 on the interstate, there's your answer. The MPG rating tests are conducted at much lower speeds, therefore resulting in the higher numbers. Also, weather, and wind conditions also apply, more wind = more work on the engine to maintain a speed.
Try driving in the slow lane for a week. Gurantee you you'll see better mileage. Lastly, if you bought the HAH for it's fuel efficiency, I'd make sure you go sell it asap and get into something more efficient, the slogan for the Accord Hybrid is "More Power. Less Gas." that alone says it all. It's hondas approach to giving the consumer more power, but using less fuel.
A Prius or Civic might make you more impressed, however it has been found that Hybrids are best in the city over regular internal combustion engines. A diesel would be good for a highway star like yourself.
