For many years, if you entered the United States Postal Service's two URLs into your browser -- sans www. -- you got bupkis:
The United States Power Squadrons at http://usps.org was always more flexible.
Finally, the USPS has decided to conform to more standard notation and have configured their servers so that any of the four variations will deliver you. The two above and the following two all work. And it only took a decade or so.
p.s. The Google spell checker supplied the following votes for the spelling of bupkis:
Whatever did we do in the bad old days to answer these vital questions?