I certainly do not have a heavy foot. I almost never use the A/C. I'm running 87 octane.
On the last two tanks (all in town) it says 13.0 since last fill-up. That's inline with the window sticker. As for the overall calculation, I attribute low numbers to cold engine temps--I bought it in December. I do use my remote start (the waste-o-gas-warm-up-the-seat-heater function), and my daily commute is less than 5 miles. I am often halfway to my destination before I have sufficient heat. (Isn't this thing supposed to have a ceramic heater to give instant heat?)
I averaged about 12 in town and 16 on the highway in my 2004 Suburban with the same style of driving. Adjusted for the new calculations for MPG, the Suburban was rated 13/17.
(Also, we have a red light at nearly every intersection.)