That post was in response to Thunderhawks' comment saying that companies should be able to capitalize on their success. If you believe companies should have the freedom to capitalize on their success, then Spotify should have that right.You paint it as if Apple saw Spotify being successful and set out: a) to develop a service specifically to compete with Spotify, and b) to put up roadblocks to hinder Spotify. I'd say that Apple Music is a pretty natural outgrowth of Beats Music, which Apple purchased as part of Beats (for a wide variety of reasons), which in turn, had its roots in MOG, which goes back quite a few years. And I don't see any changes that Apple has made to the App Store rules to stunt Spotify's growth - the monetization rules are what they've always been, and are designed to ensure that Apple gets paid (quite handsomely, to be sure) for running the store (thus, 30% no matter how the money is collected, because otherwise developers would always flock to the lower priced option even if it wasn't good for customers - calculator subscriptions anyone? - and no redirecting users to some outside place to pay the developer directly). For the record, I think a 30% cut for subscriptions is pretty high, but I can see why they do it that way (again, if the paths through the system aren't equal, the cheap one will win out).
Reading your first sentence above, one would conclude that Apple has made recent changes in the pricing structure in order to thwart Spotify's potential for success. I don't see that supported by the evidence (unless perhaps Apple has developed a time machine and used it to go back and change their pricing rules in the past). Instead, I see Spotify deciding that Apple's rules, which they agreed to (just like every other developer), are not sufficiently advantageous to Spotify's business model, so they're throwing a tantrum to try to get them changed.
Apple completely turned the music industry on its head with iTunes in the early 2000's. Apple essentially killed off the CD with iTunes. It took what? 4-5 years for iTunes to be the #1 music store in the world. That is pretty impressive considering the legal music downloading services at the time were having trouble making traction in the face of napster, limewire, etc. and the good old CD/MP3 CD. Now, fast forward to a couple of years back and a new trend in listening to music has emerged. That trend is streaming! This trend was spearheaded by Spotify (and to a lesser extent, Pandora, but I see them as a radio station instead of streaming service). This trend was not created by Apple. Apple was starting to see its iTunes service not on the cutting edge of music anymore and needed a restart. So, they buy Beats who had a Streaming service and morphed it into Apple Music. Apple Music makes Apple relevant again in the Music industry. This is all fine by me.
I understand Apple's motive and as I have written it seems all legal. The problem is that Apple has created a very successful ecosystem that favors its own apps over competitors. The way Apple has written its terms, Apple has the potential to undercut any app it want to compete against. The ability to undercut anyone they want can be considered anti-competitive by some. Spotify is at a disadvantage on iOS due to the 30% charge, which makes it less competitive. Since it is not as competitive, it cannot grow as quickly as it would have otherwise.
The issue here is not just an Apple vs. Spotify debate here. This debate has happened before with the Kindle App and I am sure numerous others. With the Kindle app, Apple just decided one day to get into the book selling business to cash in on the ebook movement and created iBooks. During this time, the kindle app was forced to use in-app purchases and pay Apple 30% of every book purchase. So, if Apple and Amazon were to broker the same exact deal with book companies, Kindle books will be 30% more expensive due to the Apple tax. That means that on iOS devices you are more likely to buy iBooks than Kindle books. As you can see this issue can apply to many different apps, not just Spotify.