Here's my two cents (possibly more, possibly less!).
1) Personally, I did a test on a $4,000 stereo system (15 years ago) and "I" couldn't tell the difference between a 192 kbps .mp3 and anything higher so I've imported my huge collection of music (about 350,000 songs currently) into my computer at that resolution to save disk space.
2) That said, I also have done PhD work into brain functioning and other woo-woo experimental areas and there's some strong evidence that we can experience frequencies far beyond the typical 20-20,000 Hz that we can hear. Frequencies as high as 100 kHz appear to be absorbed by our bodies allowing for expanded abilities like accelerated learning (I happen to have a device called an Echofone that was originally used in experiments with dolphins as well as a Flanigan Neurophone which utilizes bone conduction to experience higher frequencies and can actually allow deaf people to hear).
3) CD's record at 44.1k, however many sound processors (especially the earlier ones) end up rounding any math applied to incoming signals which reduces the overall sampling rate into the 30's (e.g., 32k). This accounts for the lo-fi sound of many synths from the 80's. This is why I used to (and will again when I have another studio) record at 96k and then reduce to 44.1k at the very end of the process. Now, any rounding will happen above 44.1k so the end result sounds full.