[toadworrier]

One of the very few things I know about audio codecs is that they at least implicitly embody a "psychoaccoustic model". The "psycho" is crucial because the human mind is the standard that tells us what we can afford to throw away.

So a codec that agressively throws away data but still gets good results must somehow enbody sophisticated facts about what human minds really care about. Hence "artifacts that are natural".