To me one of the real points of difference is that FedEx, Ups, et al will guarantee delivery by a certain day/time. Granted, the guarantee only means you won't pay the shipping charge if the item doesn't arrive in time, but in general they are very good at locating mislaid packages.

The airlines haven't added any kind of guarantee to their checked baggage charges, which would make those fees more palatable IMO.

Fedex/Kinko's needs to start opening kiosks in airports