Once it's dropped off at the post office, USPS delivers the package. SmartPost delivery time is usually a day or two added to what would have been FedEx Ground. FedEx has taken that part over in some areas, bypassing the post office and USPS.Hmm, you are correct. I do not feel like I'm truly aware of who is doing what for whom.
Did you mean USPS is taking over the last leg once dropped off at the Post Office facilities?
If not, are the post office facilities just like part of the "package highway route" so to speak and all shipping services utilize them?