I've questioned it since the beginning, it's not something Apple does by introducing different screen sizes in one launch.
Also take a look at the image in this article.
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Look at the distance between the bottom of the screen and the home button on all 3. Using 5s as the control, you can see 4.7 is making use of the available real estate by making things tighter - the screen is closer to the button. This way you keep the actual phone size as small as possible (something Apple does consistently, keeping the phone thinner and smaller). Then you get to the 5.5, and all of a sudden we have extra room to spare? With more distance between the button and the bottom of the screen? Not only that, the button isn't even centered between the bottom of the phone and the bottom of the screen. Apple/Ive/any designer would not allow something as important as the home button to not be centered, especially when there are barely any elements on the front to begin with.
Older straight on shot from this article.
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Every single iPhone button is centered between screen and bottom:
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it's a mock up not the actual thing geez chill