It's because the Civic engine is a lot more advanced. That's why it's larger and gets better emissions and performance with comparable or better mileage. Let's face it the L15 is a bit old-school.

Still, I think the Fit is the best "whole package" car. Every thing about it just seems so well designed and useful! And I agree with the above poster, I would never get an automatic in a car with a tiny I4. Saps all the power!