Ha ha, fooled ya... it's all a scam on the part of hi-fi manufacturers who have determined through a series of scientific experiments beginning at XETRA in the 1950s and continuing at various sites into the 1990s that the North American public is too bloody stupid to realise that the AM sets they're being sold are not stereo and are in fact declining in sound quality with each passing year.
The conspiracy came close to being unveiled in the late 1980s as many AM stations attempted to broadcast drivel in low-quality stereo instead of the even lower-quality monaural drivel they normally transmit. The hi-fi manufacturers were far too clever to let that happen... they just took all the outdated AM-mono equipment already on their warehouse shelves, advertised it as "AM-FM stereo" (on the pretext that, while the AM was rubbish, the FM was stereo) and the public lapped it up, too brain-dead to notice the difference.
Realising that they had been outsmarted once again, AM radio broadcasters turned off the stereo signal and went back to crappy monaural audio, then to talk radio. Eventually they were purchased by friendly lovable rabbits with no imagination like Clear Channel, ensuring that the same dreck ends up on every station as no one is listening anyway.
Having thus defeated the radio broadcasters, the hi-fi companies went on to perpetrate an even-bigger scam; buying record companies and creating a vinyl LP shortage so that they could sell CDs at twice the price of prerecorded tapes. The public has yet to clue in that the CDs are cheaper to manufacture than the tapes, confirming P.T. Barnum's adage once again.
No one ever went broke underestimating the intelligence of the American public.