And before someone tries to refute this part of your argument: sure, Android is an alternative... if you have a very niche app that somehow only caters to Android users, and somehow caters to the comparatively small percentage of Android users who are willing to actually pay for apps.

Ultimately if you're a sizeable company that wants to operate in the US, and a mobile app is something you need to offer, you have to build one for iOS. If you don't, you'll fail.

I would say these days you aren't going to do quite as well if you don't also build an Android app, but you can probably get away with it in quite a few markets if you really didn't want to.

Heh, I remember when Instagram was iOS-only, and that was the case for... at least a year? More?