Spotify has a plum position in the audio-streaming business. It’s the leading platform‚ with some 600 million users. Its 30% market share is twice that of its next-largest competitor. Spotify is adding millions of new subscribers a month‚ and few of its users cancel.  Most companies can only dream of that kind of industry dominance. Yet not even the leading audio-streaming company has consistently made money off audio streaming.  While customers love the convenience of streaming...