Simple frequency range doesn't really tell the story of a mike. Response over that range is the FAR more important spec (along with polar response and proximity effect).

The human voice has virtually no component over 18kHz... (and Don's right - I seriously doubt any of us has any significant hearing in that range at our age!). Don't get too tied up in specs. Remember, 20kHz is only one octave higher than 10kHz. So the difference between 20kHz and 18kHz is nowhere near as big as you might think from the numbers.

Mind you, if you want to splash some large for a vocal stage mic, give the Neumann KMS 105 a listen. Absolutely the best thing I have ever heard outside of multi-thousand dollar studio condensers.