The formula you so proudly point at doesn't account for all that other stuff, except in a secondary manner (yes, lighter skin means some of the other structure gets lighter, but not by 25%)
What you are unable to comprehend is that those systems are static, and the removal of the windows and associated reinforcement is a difference..
Note: the weight of the windowless fuselage vs the weight of the fuselage without windows.
What is your experience in the structural design of an aircraft fuselage?
Have you designed the structural components of a wing? of a winglet?
keep trying to defend your postion, it is rather amusing watching you flail on the hot pavement.
Isn't another reason so that rescue crews can see in from the outside?
Actually, no. Windows are required in certain locations for cabin crew to look out and determine safe exit. Hence the Airbus design I posted previously.