The trouble with the P.O. is that one hand doesn't know what the other is doing. Explain to me how one priority (2 day delivery) package can sit in limbo at one post office along the way for 2 weeks... and then start moving again. Huh? And is there any refund for the "priority" price, versus a 'slow boat to China' price? Of course not.
They promise the moon with their services, but it's "not guaranteed". Just ask any postal worker about that priority two or three day shipping and they will tell you, "but it's not guaranteed". So why claim it if it's not guaranteed...
The USPS needs some serious competition.