I bet when something does slip through unnoticed in whatever part of the EU you live, you confront the mailman with similar indignation demanding to be taxed? Have you considered becoming a professional comedian? Might cover for those monthly customs fees.
Yes, Mosaic should attach the necessary documents to their shipments, but the state gets zero sympathy from me for charging citizens for importing the occasional book or CD. At least increase the threshold from €22 to €50 or so.
If anybody is being ripped off it is certainly not the state.
PS As you said yourself, you are well off and can afford to pay monthly customs duties. If I was charged for every CD I imported it would cripple me, you self-righteous prick!