Another interesting question this brings up: How do they distribute the money from a customer who didn't use the service for a whole month?
I have to assume these companies operate on more or less the same business model as gym memberships and continue charging a large number of customers who no longer use the service but have never got around to canceling it. I only use my Spotify subscription for discovering new artists and can easily go a month without using at all or only listening to a single album since I don't want to cancel and reactivate it all the time.
I guess Spotify is just pooling my money with everyone else's and paying it out based on percentage of total plays even though I didn't play anything that month.