This graphic shows the increase in streaming use in 2014, pretty impressive numbers from a percentage standpoint.

Infographic: Streaming Boom Changes Music Landscape | Statista
You will find more statistics at Statista

What does that mean from a dollars point of view, however? And if streaming pays less than traditional sales methods, what does it mean for the artists, rights holders, etc? For that, here's another Statista graphic:
Infographic: Digital Accounts For Nearly 70% of U.S. Music Revenues | Statista
You will find more statistics at Statista

That's still a percentage-based graphic, however, which doesn't answer the real question--who's making money in this new music industry model? One last graph, to show that in country music, at least, they're taking it to the bank--this isn't just album sales, however, it's overall income:
Infographic: Country Music Acts Earn Staggering Amounts of Money | Statista
You will find more statistics at Statista

My bet? It's the traditional record labels who are still making the majority of the money in the music business...the digital transformation may have taken them by surprise kicking and screaming into the new millenium, but they still own the rights, produce the recordings, and their lawyers are still the best at screwing over the actual artists, the musicians and songwriters who really make the music we all listen to, however we get it delivered to our ears.