I respectfully disagree. The average courier for both companies do the same thing:
They get in their truck, drive, deliver and/or pick up packages, have lunch, continue to deliver and/or pick up packages, then call it a night.
Of course there are subtle differences. There are subtle differences even within the same company depending on the station. Subtle differences aside, it's the same job imo.
Being a Postal courier is different (yet similiar in it's own right). They walk their routes, don't have handheld computers giving them updates on pick-ups, almost exclusively deliver envelopes and mags, etc....