Generally speaking, voice communications has very little to do with frequencies above 8 kHz. The same is true below around 300 Hz. The critical range to understand speech well is around 300 Hz to 3400 Hz. So that's what they test...
I was assuming that if you have already lost all hearing above 8 kHz, this is not a good sign for your future ability to hear in the voice range. Perhaps this is not justified, although the person I mentioned earlier has deafness in her family.