Yep. One major difference is that with Google/Apple (and also Steam I believe), app makers can at least choose the price of their apps and services themselves,

Yep. One major difference is that with Google/Apple (and also Steam I believe), app makers can at least choose the price of their apps and services themselves, and they know how many units they sell. If Google/Apple are charging you 30%, just increase your price. With Spotify, however, musicians can't choose how much their music is worth, and the payment of royalties is also not exactly transparent.