None of those examples removed functionality from other applications.
Neither does the cited camera app. When you're using the camera, the button does one thing. When you're not using the camera, it does something else. Nothing has been removed. Things have only been added. The concept of using one button for multiple actions has been around for as long as computers have had buttons. This is especially prevalent with console games. When you're on one screen a certain button has a certain action, when you're doing something else that button does something completely different. It's all about context. People are in fact intelligent enough to figure this out. Yes, even Apple users.
It does remove functionality. You can have music playing while you're doing other things, i.e., using the camera app. If I'm not using the POS apple headphones with built in volume controls, I have no way (other than using an experience interrupting pop up window) to change the volume of the music while using this camera app. How is that not taking functionality away? I'm not saying banning the application is the right choice, but there is logic to the decision.