>> Admittedly, Android does it much better by providing oAuth, an easy way to get the users sign in, and of course APIs for almost all the popular features.

First of all this has nothing to do with iOS/Android. This is an app trying to access a web service. Apple needs to provide oath or similar for accessing their iCloud services.

>> And also, for installing $0 apps you don't need any credit card details at all. Even the buttons are different "Install" v/s "Buy".

This is untrue. I couldn't download any free apps until I had setup a merchant account with credit card.