The App Store is packed with apps because developers saw an opportunity and wanted to seize it. Everyone's in it because it serves their interests.
The iPhone released without an App Store. Their original plan was very clearly to limit it to web apps. Apple, including Steve Jobs, spent a lot of time and energy explaining why web apps were the best option.
And then Apple realized, largely through apps developed for jailbroken phones which led to a lot of people jailbreaking their phones, that for iOS to really succeed they needed apps.
Windows Phone 7 is another example of this. It was a superior OS to iOS by most measures. It died almost entirely because of the lack of major apps.
If major app providers (Google, Spotify, Netflix, etc) had never made their apps available on iOS and had made them available on Android instead iOS would probably be looking like Windows Phone 7 right now.
I'm torn in all of this because I'm not much of a fan of either company.
They literally do consider it nothing. I've talked to some of the devs that were responsible for implementing it and they consider it entirely a spam prevention measure. They determined that $100/account was a high enough bar to prevent people from creating hundreds of them and doesn't have the overhead of manual human ID verifications.
The most recent numbers I can can find is that there are 34 million registered devs which is a cool 3.4 billion ARR and that is 0.89% of their $380 billion revenue last year.
It says a lot that the €100 developer fee (I'd imagine Spotify pay for multiple licences in multiple countries) that Apple consider it nothing. It probably is 'negligible' given the size of Spotify but also don't even consider highly popular apps like Spotify 'contributing' to App Store ecosystem that has also helped Apple.
Their press statements are starting to become more and more snarky. They would do better to keep their chin up and keep going. This sort of snark is more befitting of Ryanair than Apple.