That's true, but when op says that, I assume they don't mean any $50 headphones, they mean the best (lets go with least harmonic distortion as our arbitrary cri

That's true, but when op says that, I assume they don't mean any $50 headphones, they mean the best (lets go with least harmonic distortion as our arbitrary criteria for "best") ones you can get in that price range, and for the most part they are describing a trend that DOES exist to some degree in almost any category of physical good you can buy, from power tools to kitchen appliances.