The ear is about the worst auditory measuring device there is. It has almost no memory. If there is any amount of silence between auditions probably half of the ability to hear a difference is gone. That said, there are things that can account for why people hear differences between devices. One is impedance. Speakers and amps can perform very differently based on the output impedance driving them. Some equipment is obviously more sensitive than others. There is also of course phase distortion, which can change the way transients are perceived and how frequencies interact across the audio spectrum. Of course the big one is harmonic distortion, which has the side effect of sometimes being euphonic, and other times not. The most coveted devices in pro audio are chosen not for their linearity, but for their large amounts of phase and harmonic distortion, because it sounds "musical" or pleasant. A DAC is not a device that usually benefits from such non-linearities.
Of course this can all be measured, and since a slight difference in volume is enough to make two otherwise identical devices sound wildly different, I don't see that there's much choice but to trust measurements when comparing hardware, especially when the differences are well beyond the limits of human perception as sis the case here.
I agree, that most of the differences heard are in the listener's head. Heck, listening to the same song on the same system first thing in the morning can be a totally different experience than at night.
I'll say this, I doubt 99% of audiophiles can repeatedly pick out the differences between two properly designed devices simply by ear. For those of us that want the best of the best, just because, measurements are the best way to find it.
