You have proof of this statement? If that really is true, then 120Hz would receive a very bad rep. I've not heard this though, and only seen good reviews of the 120Hz HDTV tech, and the demoed 240Hz HDTV.
EDIT: I did some looking and found out that they do use something similar to what you said, but it's not just "Take this image and copy it to scam people into thinking they are getting twice the quality". It's about the 24FPS of film and having that fit neatly into a television.
Old sets and most modern sets have a refresh rate of 60hz which does not divide well with 24. By changing the refresh rate to 120 (which is a multiple of 24), it allows the natural film rate to process correctly rather than the stuttering that came with trying to divide 60 or 30 by 24. I don't know the rest of the technology mumbo jumbo, but according to this, I don't care if it is just showing a black screen or copying screens. If it is showing the content more clearly, isn't that what it is meant to do? Plus the new technology doesn't cost hardly any more than the older 60Hz tech, so I don't see it as a marketing ploy. If they were trying to sell 120Hz 1080p HDTV's for $500 more than the same size 60Hz 1080p HDTV, THEN I would see it as all a marketing ploy.