Then how unreasonable is $0/month for radio? I'm happy there's people who can look at services like Spotify and Rdio critically, but I don't think appeals to intuition like "that can't be right?!" help us much.
Because radio is not a substitute for recorded music. The inability to choose what you're listening to was always the stick that compelled listeners to purchase a recording. If you have Spotify, there is no reason to ever purchase that music in a download store.
Fast, reliable, and unmetered wireless is by no means ubiquitous. There is still the benefit of being able to play offline, burn to CD for the car, share with friends, etc.
Admittedly, the incentive to want offline music may continue to diminish over time.
Radio may be far more interesting that you expect. Once upon a time you had Payola[1] where radio plays were designed to influence record sales in a nontransparent way. Now you have the issue of consolidation where you'd have no idea which plays were influenced by royalties etc.
Anyway, my point is that your comment could be interpreted to mean that radio is democratic and it is a democratic way for meritorious music to be elevated.
By democratic I don't mean anything more virtuous than screaming masses, but I don't think commercial radio even rises to that.
Anyway, I have to read more to get an overview of how Spotify and others compensate the talent that makes content, or even cheat them, but I also want to make sure that popular radio isn't treated like something we'd prefer.
Because there is not such a thing like $0/month for radio, as you are forced to hear ads, and the advertisers pay for it, and you are forced the songs you hear, witch some people paying for controlling it.
Yes, in the old days some companies controlled which music was heard and which not, and those gatekeepers were not as cheap as you thing.
Radio is like an ad service for the music industry, where you listen to demo tracks and hopefully buy the full album. Rdio and Spotify give you full access to the end product for virtually nothing. It has totally screwed up the perceived value of albums.