Weight does play a huge factor here.
Honda worked hard to get the Fit under the green rebate program the gvt had.
Toyota had the Yaris included in the program.
Both cars have very very similar engines, the main difference is weight.
Plus, diesels feel more powerful in real life than any gasoline engine. Like for me personally, when I drove the '06 Jetta TDI for the first time, I was stunned. That little diesel pulled like a pro, it was really amazing. Gasoline engines are picky, you gotta be in between 4000-5000rpm to get the max outta the engine. Diesels? 1500-4500 brute force. They're just more drivable in everyday life. You can go from 30-130 in 3rd
. And those 240lb-ft torque move the car with attitude.
I still think one could get the TDI into low 5s high 4s on the highway w/o a sweat.