Calibrated (my Audyssey is +-1DB 20hz-20khz) mics do exist and calibration files do exist for some mics, plenty good enough considering how terrible the average house/apartment room is.

Your totally right about room treatment and why I don't spend more than the budget end of HiFi, because I know how terrible my room makes everything sound..

Ive measured a few rooms and sets of HiFi and the biggest issue I find is not the general frequency response, but room modes, they peak far more than even the frequency response from a cheap boom box. Without active EQ or a notch filter and extensive room treatment then trying to flatten out the response of a speaker is futile if you ignore the room modes. Add in transient and phase responses and you add additional challenges to getting good audio.