Gas mileage in a vehicle has a lot to do with how you drive it, but more importantly is how well matched the engine is to the weight of the vehicle.
I recently test-drove a Mazda CX7. The mpg figures are in the same ballpark as my current vehicle - the Honda Element - averaging about 19mpg. But the performance difference is staggering. The CX7 has a smaller engine but it's turbocharged and that makes all the difference in the world. It's not sluggish. It doesn't bog down going up long inclines, and it just feels altogether more peppy. Well - with a turbo, it would, but the 6-speed automatic gearbox helps too.
So I figured it was the turbo and the lighter vehicle that made it more zippy to drive (I can't bring myself to use Mazda's "Z" word). Well - not so much. The quoted kerb weight for an Element is 3640lbs for the 4WD AT. For the CX7 it's 3930lbs - about 300lbs heavier.
So a smaller (albeit turbocharged engine) in a 300lb heavier car, with 6 gears instead of 4 and returning about the same gas mileage, makes it an infinitely more driveable SUV than the Element.
And this is the problem with the Element overall. It's a wonderful vehicle - totally practical and fun to drive, but it's just out of breath all the time. The engine just isn't up to the job because it's a normally aspirated 2.4 engine from the Civic and Accord. What Mazda did was realise they were hauling a heavier vehicle around and adjust the engine accordingly. Honda didn't. The difference is like night and day.