timdoyly,
Many manufacturers confuse issue by quoting attenuation figures in a range of inappropriate? frequencies.
First off I won't admit to knowing much about ANR headsets. My thoughts on why the manufacturers quote attenuation figures in a range outside of human speech is because that's where all the noise that we don't want to hear is.
If the frequencies that human speech typically occupies were attenuated, then the ANR would filter out human speech. That's the part they want to leave alone. As I said though, I'm not an ANR expert or anything and await correction if I am wrong.