I wouldn't consider some of these flops at all. I still use the infamous MiniDisc WEEKLY, and you know what - not one has failed on me since my first one in 1999 - can you say that about the cassette format it replaced? Compact, superb audio codec, very NON-MP3 sounding - and barely noticable difference than an actual CD. Eraseable, on the fly edits, text, inexpensive media, no computer required - one of the best items Sony ever devised. Not a flop in my book. IT WORKS - can you say the same about AM-HD and it's neighbors on the dial.
Same for the original LaserVision VideoDiscs - they worked and had great audio and video. Sony's OLE TV's are spectacular, they work, but just too expensive; however, the OLE screens have made inroads on small portable units where they ARE cost effective and they work.
So, you have to define 'flop'. Is satellite radio a 'flop' as ONLY 20 million folks are paying for it? DVD-HD's - a flop? Some of the best (or better) technology is considered a flop, but when it works, it works well, so I consider "C-QUAM AM Stereo" a 'non-flop' as it worked, worked well, forced better AM tuners onto the market and AMAX would be the standard for all AM radios IF the FCC would have made a standard in 1982 instead of 1992.
The success of HD radio, and AM radio in general, is unique, compelling progarmming, niche formats and local programming - offer for 'free' on a radio what people want - without a $65 bill every month for their 3G cellphone or internet access. Great progamming on a portable radio that runs on a 9Volt battery never went out of style with me, or even my teens - when it's something that they really want to hear (even Radio Disney, I hate to admit).