I think another difference is that the bulk of FedEx and UPS customers are businesses -- who typically are smart enough to allocate business among at least two vendors. Short-term this keeps your suppliers honest on price and service. Long-term it hopefully sustains more than 1 supplier. Even when an industry has one "gorilla" (e.g. Intel), business customers will try to sustain at least one "chimpanzee" (e.g. AMD).
However this dynamic is missing from consumer businesses.
However this dynamic is missing from consumer businesses.