I dunno man, Apple's PCB designs are incredibly space efficient. Compare the sandwich PCB of a modern iPhone against the main board of something like a Samsung Galaxy. Apple is sweating out every cubic millimetre it can, while Samsung is perfectly fine with a load of empty green PCB all over the place.

Apple definitely refurbs boards. They just don't do it in the back of an Apple Store. It's far more economical for them to do full logic board swaps (or other components) than spend the time and effort doing component level repairs in the back of a retail store.

I have seen some Apple ][ motherboards with jumper wire(s) hidden on the back side.