When the Pandora music service launched, I remember reading about how it worked (predicting what you might like next) and it explained how they don't need to know anything about the songs at all (such as genre, tempo, instrumentation, place of origin, year of release, language, etc.) to predict what else you'll like. They simply identify other users with a similar history to you, and deliver to you some of the stuff that those other users had listened to that you hadn't listened to yet. If you abandon a song (suggesting that you don't like it much) then you become a bit less associated with the users who play that song a lot.