Starbucks is interchangeable with any of the many coffee chains. The service is fast, prices won't be insanely high, yet it won't be stale coffee sitting for days in a warmer.
So I'll choose Starbucks over a boutique artisan coffee house and over a gas station. But Starbucks vs Other_Coffee_Chain means nothing to me. EDIT: What I mean is I don't "decide to get my coffee at Starbucks". I decide I want to go for a walk and get coffee and I'll probably stop at the closest coffee chain.
Anyways, to bring this analogy back, what is the Spotify value add? The technical competence to host files on the internet? Putting a front end on CDN hosted media?