Should the definition of post-haste be changed?

It means “with the greatest possible speed or promptness” and is derived from the speed and efficiency of the postal service. But anymore, if you want something done with the greatest possible speed or promptness, the post office would be your last choice. With so many alternatives for letters, like e-mail and fax, and packages are delivered no quicker, efficiently, or with the best cost than FedEx. What Fed Ex could do in two days, the post office will charge you twice as much on a “when it get there, it gets there” basis. So it seems that logic would dictate that when someone asks for something post-haste, it should be done slowly, inefficiantly, with more cost than necessary.