JasonSobel:
First of all: Sorry if you are upset by the first part of my response, since it was not my intention to offend you.
I will try to explain my viewpoint to Freelunch and you (and, or course, to anybody interested in), which is not an easy task for me in a foreign language. My purpose is just that, to explain and try to add something to the forum, nor contradict nor spend your time.
That said, the upper frequency limit of hearing is not somewhat arbitrary, but a scientific data totally stablished through neurophysiological recordings. There is no sound perceived beyond, lets say, 20.000 Hz, as there is no vision in absolute darkness.
The perceived sound is the result of the different sound waves, each with its own frequency) reaching the cochlea in the inner ear, where they stimulate the "hair cells" of the Organ of Corti and are transduced into nerve impulses that reach the auditory cortex. It is here where the perceived sound arises.
When we hear the sound produced by the A violin string, we are hearing the fundamental note (A), plus the first, seccond, third...harmonics. They are the responsible of the violin timbre. Since the frequency range of the violin is 196 to 3.136 Hz, we can hear even the second harmonic of the highest note, but not the third. The perceived sound in this case is the result of the highest violin note plus the first and second harmonic. The third harmonic (approximately 24.000 Hz) is not audible at all, and does not contributte anything to the perceived sound. The same repeats with a concert piano (frequency range 27,5-4.186 Hz, flute (261-3.349 Hz) etc, etc.
So, it again looks like more important the microphone response in the 20-40 Hz (audible) than in the 20.000-40.000 Hz range (not audible at all, nor contributing to the perceived sound).
I have no dout that the Sanken CO-100 K microphone is a wonderful microphone, but nor hearing phisiology nor psychoacoustics support that the extended frequency range 20.000-100.000 Hz) is responsible of it. You have guessed well, this microphone is not for me, perhaps for nature recordists interested in bat ultrasounds.