Given the kind of draconian control apple has on its store, there is always a risk if you are part of the ecosystem. But earning half income is still better than none right? Besides now windows has app store too and a much bigger distribution. If you don't like Apple's terms and your other platforms are making enough money you always have an option of kissing goodbye to apple. My point is that diversification gives you options.

Both androind and Windows provide guidelines to port over your applications over. So I don't think this option exists only in practice.