Default Keyboards; Different Perspectives
With iOS 8, iOS and Android users have the capability to install non-standard keyboards. A key difference in the implementation Android has over iOS is the ability to set a default keyboard.
In Android’s settings, “Language & Input -> Current Keyboard” identifies the default keyboard that will be presented at all text input boxes.
In iOS’ settings, “General -> Keyboards,” all keyboards that are installed are certainly listed, but pressing the edit button and reordering them does nothing to change which keyboard is the default. Moreover, for input fields that deal with passwords, as well as text entry fields in non-app environments (Springboard, and Settings), iOS will present the standard keyboard and prevent switching to an alternative.
Apple’s distinction is that an alternative keyboard might be suited for occasional use, but, for the vast majority of the time, the built-in keyboard is suitable for all users. This is exactly the same thing they say about alternative browsers: You can install Chrome, but Safari will always be the default link handler.