Most off the shelf mass market hi-fi may not be able to reproduce higher frequencies, however it is quite easy to source tweeters that have a good frequency response up to 40 KHz which I have tested and used in the lab (admittedly not for the purposes of reproducing music).
Similarly whilst many PA power amplifiers 'boast' that they filter everything above 22 KMz it Yamaha at least make ones that are reasonably flat up to 40 Khz and have useful output almost up to 100 KHz.
Whilst you may not be able to 'hear' above ~20 KHz it is still possible for many people to percieve something well above this. My boss can tell when our air-coupled ultrasonic transducers are operating even from a distance, and they are typically operating above 160 KHz. with a high-enough burst reppetition rate I can 'hear' if they are working when close up.
There is a clear difference between my £400 hi-fi and my friend's £40,000 system, but I have better things to spend my money on. Also I have some CDs that on his system are terrible to listen to becasue of the quality of the recording, which sound fine on my system.
Biting the hand that feeds IT
