All of which didn't cost Apple very, very little. They didn't spread word of Spotify across the internet, didn't make it somewhat of a household name. They provided the platform, ran it through a quality check, and gave it a spot on the front page of own app store. It was Spotify who had to negotiate licensing deals with all the various record labels, build the infrastructure to support potentially millions of people streaming millions of songs through their service without any hitches or hiccups, had to spread word of the service. That costs them considerably more, and Apple taking a perpetual 30% cut of their subscription fees, their lifeblood, isn't kosher in my opinion.
I can understand them taking their 30% off apps bought through the App Store, but subscription services are another matter entirely. Think of it in terms of iTunes and the iPod, which didn't become a massive success until it was made available on Windows. Does that mean MS deserves a 30% cut of all transactions made through iTunes? They're providing the platform after all. They're the ones putting it in front of what was then a much, much larger market than what it initially had. I'd still say no, because MS is merely providing a gateway, and iTunes added value to Windows at the time. It's the same situation for Spotify and Apple.