Spotify has achieved what no normal entity could. Go them for having a relatively decent free to play with, I'm assuming, a good pay to play model as well.
In Canada, one of the major wireless providers offers Spotify premium accounts bundled in with mid and high tier data lines (i.e. 2 years of Spotify premium "for free"). So I wonder what other providers around the world do this, and how many of the 40mm are part of this group.
I have accounts on both Deezer and Spotify because of bundled accounts on wireless providers. So far I prefer Spotify but only because of the Discover Weekly feature.
Free to play won't be around long imo. Since Spotify first launched for me in 2009 the free offering has got progressively worse. The second the labels can drop freemium they will and I don't think we're too far away from that.
I haven't used Spotify free in a long time but originally the only difference between free and premium was ads and offline mode. AFAIK there are many more limits on free now.