Lowpass filter

Do you refer to commercial mixes which look like they have a very steep low-pass filter at about 18 KHz applied when you look at them using a frequency analyzer? I wonder what purpose is behind this?
 
it's just pleasing to the ear that way. Try eqing those top frequencies back in and it just doesn't sound nice.
It's quite rare you'd ever have much of that super high top end anyway. I recorded a kit recently with a pair of neumann TLM103s as OHs, and even the cymbals start to tail off over 16khz (not to say they dont have any, and that that region isn't important ofc)
 
with the sounds im getting, there's not much past that area already, so no need to cut

i do find my self using a hi shelf boost to make up for the lost highs when gooing from 48 to 44 tho