With e-mail replacing so much mail, the post office is desperate for new business. So they've been cutting deals with the delivery companies to handle the last leg. The post office has much denser daily coverage than either UPS or FedEx, which means that often they can do the last leg more cheaply. It might mean that for something like UPS Ground delivery, which is advertised as 1-5 days, it may increase the average to be closer to the 5 day mark, but that's all you're paying for anyway.