This is a long overdue case.
1) Apple having the only valid store is a good thing. That is not a problem.
2) Every in app purchase in its store going through Apple in itself is not a problem.
However, when we combine these 2, some questions arise about monopoly.
At the same tine, this does provide customer security benefits. For example, if I pay some app in-app and the app does not work, Apple will not be able to guarantee any refunds. Apple also cannot guarantee if a $1.99 purchase, will actually be charged $99.99. This will totally create a set of apps that are absolute scams and Apple or customers wont be able to do much about it. It looks like a monopoly, but the consequences of removing these measures will kill the iOS ecosystem.