For me where I am they use UPS and once they actually ship it gets here in a few days, but even prime orders don't seem to bother leaving the warehouse for a week or more (for in-stock things). It's like every order is now "Amazon day orders" or something.
yah they play the whole get a $2 digital credit or whatever for orders. It kind of blurs the expectations too when now it's becoming the norm for things not to meet the 2day shipping expectations that is prime. Things are also blurred in the opposite direction with same day shipping or one day shipping on certain items. It's the inconsistency that's confusing and kind of invites you to stop guessing and just patiently wait like the old days of ordering something through the mail.