The idea that it can only make a difference if people measure it is absurd. People buy Apple products because they look nice and work well. Shaving space and weight is part of their design. I know people buy iPads instead of Galaxy Tabs because of the industrial design. I seriously do not believe that the iPad could have such a nice design if it was fully modular. I'm sure you can come up with a bunch of individual components to modularize without substantially impacting the design, but that doesn't do us any good. Unless I misunderstand your complaint, they'd have to modularize many components, and that will definitely impact the design.

In my experience, people are mostly surprised as Apple's good service when they need a repair. It's not like other manufacturers provide cheap repairs, either.