Quality is important if you are the gatekeeper trying to sell other people's music. But if I am an artist, and I record something that everyone thinks sucks, so what? The only consequence is a low rank in the aggregators, just like low-quality submissions here on HN.
Well there is the "cost" of having an unwanted item clutter up the aggregator (or store, etc.). Things like collaborative filtering help with this, but are still (shockingly, really) not used, even by HN.
