If there is no appreciable content which is audible to me above 16k (or more reasonably 15.5ishk for the passband), I see no reason to keep it around, especially material intended for playback and not further processing. This is still relevant for portable devices at this point in time. When we all have 2TB flash storage in the palms of our hands, carrying around lossless 24/96 masters will seem more reasonable. For now, I want to hear only what is audible to me, and nothing more, so long as the loss of that which isn't audible will be palliative for storage.I'm afraid I don't understand the hearing aid argument. How many sane people are going to pay for an implant so that they can hear a few kHz higher than 20? Certainly not I.