If you want me to take a stab at this I will have to say that the scope with the larger objective perhaps just has a better optical design. I know that you stated that you felt both were equal in quality (glass and coatings) but that doesn't mean that the design of the optical system is the same, especially given that we are talking about a fixed power vs. a variable. Just because a variable has more len's doesn't mean that it can't or won't resolve an image better. Some of the more expensive scope these days have more len's in them to sharpen image quality, be it brightness, resolution or contrast.