If the Spotify Premium subscription was $4.99, you would easily get twice the number of subscribers, and hopefully even more than that. More users is worth more than revenue in the short term, because increased number of users means higher potential for new subscribers. PLEASE think about it.
There are many users on the fence like myself who would subscribe at this level instantly. At the moment I just cannot justify it at $9.99/mo when services like NetFlix cost $7.99 for unlimited streaming of movies.
"You have nothing to lose but the free-loaders!" :)