They -can- emit higher frequencies with better fidelity (and DR), however that's a product of mastering the CD, not something that need occur in the CD by its very nature. So the way you're stating it is incorrect. A CD can replicate anything a cassette/vinyl can do (that is perceptible by human hearing). Now whether industry respects that or not is up to the company/band/whatever making the CD and what they choose to emphasize.