I get what you're saying. I'm a classically trained pianist (and this may be the problem) who has recently taken up the cello. When I'm tuning my instrument, a note on an open string appears to my tuner to easily fluctuate by 4-6 cents. (That is +/- ~2-3 cents.) The article mentions that the tunings often vary by just about this amount. (Some were larger, but many were not.) My ear certainly doesn't hear the fluctuation in pitch that much, and I'm trained (spent 2 years in music school at the university level, had honors theory). When I'm fingering a note, it can vary by even more, even when I don't think I'm moving my finger at all. It seems to me that typical listeners would have a hard time discerning those differences, though I suppose the differences are amplified when played with other notes.