> ...it's a tempting hypothesis that there is a relationship between the acoustic properties of human speech and the physical/neural structure of the auditory system.
This seems trivially true in the sense that human speech is intelligible by humans; there are many sounds that humans cannot hear and/or distinguish, and speech does not involve those.
Yes, but at the least it's a bit more than that, because the ear is more sensitive to certain frequency ranges than others, and speech sounds seem to be more clustered in those ranges.