The streaming-music business reminds me of Netflix in its early days, before movie studios became worried that it was cannibalizing rental/VOD revenue for new releases. There are a certain group of fans who are willing to pay $10-20 per album for access to music the moment it's released. With Spotify, those fans are treated like any other stream even though they're willing to pay more. It's inefficient pricing, except from Spotify's perspective as they're able to use immediate access to new release music as a lure for subscribers. So really, you can look at Spotify as capturing that demand and converting it into free advertising for themselves. I don't see that as sustainable in the long run. Some artists are already holding back new releases from streaming services. Like Netflix, I think that in the future you will see few new releases from popular artists until they've been available through premium services long enough to capture demand from hardcore fans.
Spotify treats all songs as if they have equal value, but that's obviously not true from the listener's perspective. For any given person, there are going to be some songs that they're willing to pay a premium to hear, and some that they'll only listen to if it's free. Spotify is a good deal for the latter case, but not if it offers a discounted version of the former to people who could pay for it. Just because Spotify counts every stream as a single interchangeable unit of value doesn't mean that listeners value every stream equally.
I think Spotify is in a great position right now, they are building up a huge userbase right now (first step for Facebook etc. too). But the service will monetize very well. For example I would pay extra per album to get to stream a couple albums on the day of their CD release just because it's convenient to have all my music in one application.
Or charge me 15$ a month for a gold account and add a feature on the artist page to leave a 1$ tip. This extra 5$ goes into my "wallet" that I can then disperse straight to my favorite artists each month. Like a microtransaction.
Spotify treats all songs as if they have equal value, but that's obviously not true from the listener's perspective. For any given person, there are going to be some songs that they're willing to pay a premium to hear, and some that they'll only listen to if it's free. Spotify is a good deal for the latter case, but not if it offers a discounted version of the former to people who could pay for it. Just because Spotify counts every stream as a single interchangeable unit of value doesn't mean that listeners value every stream equally.