Since Sweden adopted anti P2P laws (IPRED) in 2009 Spotify usage has grown. In 2009 France adopted an anti P2P law (HADOPI). Since then music sales in France declined at a lesser rate than global sales and therefore artist earnings declining less than on global level (http://www.fortherechord.com/hadopi-and-cartes-musique-franc...). This would point to a correlation between "piracy" and music sales.
1. Pirate 100 albums in a year, buy 5 albums, yielding $7.50ish collectively for the 5 albums.
2. Listen to everything on Spotify, play 2000 tracks, each paying 0.2 cents per play. $4 is spread amongst everyone.
A fall in "piracy" doesn't necessarily cause (or even correlate with) overall earnings to go up.