Perhaps I should provide some research to back up my claims. However, it would appear that above 20kHz, or 22kHz, or 18kHz, or whatever high point you accept as the top of normal human hearing, those extra high frequencies aren't detectable unless by direct contact with the source.

Whether or not you would consider air to be a suitable direct contact source, you might accept the idea of non-detectable fluid pressure having a physiological or psychological effect on the human body. The same way infrasonics can be used as a weapon against humans, and is the reason for "spookiness" in old houses.

High frequencies are also very important for localization, hence the bat's hearing and "speech" range. One might argue that _if_ humans can perceive higher frequencies, whether or not they consciously realize it or not, then localization would improve. Thus improving imaging in audio reproduction.

Ultra Hearing Fetus
Ultrasonic Hearing in Humans: Applications for Tinnitus Treatment