"Because people have no problems in the classic quiet room, one person talking sound test environment, it tends to slip through the simple screening tests."
This is exactly why every time I've had an Audiology test, I've never scored above "Average - Above Average", even though I can hear nearly every fluorescent light ballast, powered-on TV, etc. From my own personal tests that I've done with soundwave generators, I can hear up to about 20khz.