TechCrunch has a great post that covers streaming royalty costs, plus some interesting information on the most active streaming sites on the Internet, including Spotify.
Like all webcasters, Spotify must pay a per song fee for every song they play. These range from 1 cent per play (for interactive playback) to 0.2 cents (radio experience). While the rates seem modest they add up quickly. 10 million streams per day translates to $100,000 per day, $30mm/month and $360 million annually in royalties - just for the UK operation. Royalty rates are similar in other countries and its Spotify claims 1mm users from Sweden as well. Advertising from audio and banner ads cannot generate even a sizable fraction of these royalty obligation….
… Ad rates cannot generate revenues sufficient to pay even the mandated royalty rates much less all the costs of running a high tech business.