So...yeah...this "2%" thing is interesting...
We traded in our Nissan Xterra last year on a Toyota Prius. My cargo carrying hasn't really changed much either believe it or not. To carry my model airplanes in the Xterra I had to fold the rear seats down (and take the bottoms out and leave them in my garage). In the Prius I just fold the rear seats down (no seat removal needed) and load up my planes. These aren't little planes either - we're talking from 55" wing spans for the small ones to one with an 81" wingspan. I usually carry 3 planes out to the field with me. As far as taking car of my home depot runs and such - I haven't had to buy anything yet that the Prius couldn't carry. The cargo room in an Xterra is generally lacking however so this isn't really a testament to the Prius in that fashion. I do feel like it's easier to get the boy in and out of the carseat in the Prius because I don't also have to climb up onto an SUV to do it.
I digress; The point is that the Xterra has an 18 gallon tank or so and I would get if I was lucky 250 miles to the tank for an MPG of 13.8 mpg. We'll be generous and say 15.
The Prius usually takes about 9.8 gallons for a fillup, lets go ahead an say 10. I usually get about 450 miles for that tank.
That's a 300% difference in simple miles per gallon.
I'm doing my part.
Flame on compadres.