On the Amazon application, there is no navigation bar below, so the Home bar has jumped to the top of the page.
With Twitter, the content is full in the screen and the space above is very nice.
The icon below is taken by the Home bar, so it is very narrow.
Like many other Apple apps, there is plenty of space underneath the keyboard of the Messages application.
Like many other apps, Facebook's navigation icon also has to make room for Home, so there's plenty of space.