about music:
imagine how much cost a cd physically. lets say its 5% of the price in shop. what we get more, the promotion cost. and so on and so on. basically the cost to produce a cd is much less (or could be much less, due to big companies) than a price in shop. that leads to piracy. todays music is based on the quantity, not quality.
about movies:
id say, compare the price of cinema ticket, to a price a single dvd. just a laugh.