Pandora apparently pays 12 cents per 100 plays. At that rate, they are paying out $1200 for a song with a million plays. If the artist only gets about $16 (under 2%) out of that, where is the rest of that money going to?
Well, to the artist for one. He's not being payed as the artist. Before his place in line you have the copyright owner, the lead performers, background performers, and the other 60% of songwriters. Yes, that's right: he's complaining just about the size of the 40% songwriter's cut.