What's from stopping someone else from making a few $5 knobs and selling them for 100 times the price? I guess the major caveat to that idea would be that they won't be the same "reputable" brand of knobs that audiophiles know and love. A getting rich quick scheme would involve leverageing from something else that has made you popular.
I'm surprised if any of these companies haven't been sued by the naysayers, for the dubious claims they make for their products.
At least there's some justice dealt with Monster. They may be far from audiophile brand, but their stuff is still badly overpriced. Gizmodo made a comparison with a monster cable and a coat hanger wire, and the quality of sound transmission can't be distiguished in blind tests. (of course coat hangers are not very impractical being solid core wire but that's beyond the point of the experiment) Employees in electronics/audio retailers get more comission for selling Monster products, which is why they push them aggressively towards the customers.