I believe Fed Ex sends all their packages to their Memphis hub for sorting and delivery. Works well for them.
I don't know it's it still true today with all their "ground" and "2nd day" offerings but their next-day deliveries all pass through the Memphis hub in the middle of the night.
I recall hearing stories about people moving to the Memphis area and getting a GREAT deal on a home in Southhaven, MS....except they didn't realize that they were directly south of Memphis's 3 parallel runways until the first night they spent in their new home.
It has been successful for them.
The USPS was built and designed for local letter delivery. Treating local correspondence like overnight nation wide document delivery is not cost effective.