I'm almost certain free users pay out a lower rate, payout information from Zoe Keating has confirmed that there is a somewhat large disparity between rates even within the same country with no explanation attached, there's only 1 or 2 things it could be. Radio payouts are lower because it constitutes a 'radio play' and therefore gets less than a premium user playing the song on demand so there's definitely variance within the payout rates.
I think there certainly is a lower rate for radio -- I think Spotify gets Pandora-like rates for Spotify Radio, which I believe are lower than the rates they pay for their normal music streaming. I don't think there are different rates for free and paid streamers, though.
