Your statement has no basis in fact. Please go look at the distribution of MPG's shown on Fuelly, and compare the average MPG there to the Combined Fuel Economy number shown on the window sticker that came on your car.
Let us know where you get the data that a majority of owners are well below the MPG's stated on the window sticker -- do you have more data than shown on Fuelly? Right now it is 211 cars tracked over 1.5 million miles, and includes engine break in for many or all of those cars (since most people I know that are on fuelly have tracked since new).
You can also ask them, many of those Fuelly vehicles belong to NASIOC members that are posting here...
My car is no longer on Fuelly, but as stated I am at 27.99 MPG overall, including my lower than average numbers from driving on snow tires this winter (the first winter it had yokos on).