There will always be people with slightly wider sensory perception than others, but are you honestly saying that you can easily hear sounds "well above" 20kHz? Have you tested this in a double blind test? I know that sounds like a lot of effort, but it would be interesting. You would be somewhat unusual if you could hear, say, 22kHz.
If you test this and hear something, it's almost certainly because the ultrasonic signal is being distorted by your amplifier and speakers and you're hearing distortion products that are ending up at frequencies you can hear.
As he mentions, with 16-bit it's easy to significantly reduce the dynamic range or clip; you only get the full 120dB range of 16-bit with careful handling and calibration. You don't have to worry about all this with 24-bit - you'd almost have to deliberately screw up the signal to reduce the dynamic range below that of a human's.
Ideally audio engineers would take the effort to do good 16-bit conversion for distribution, but I realize that's too much to expect of them.
24 bit is also extremely easy to hear. Arguably more important during the recording phase when headroom is valuable.
Its just as easy to qualify everything with "placebo effect", as it is to be dismissive