It's true of android too, you're just used to it. Even Graphene eliminated the back button, and makes you swipe left from the right side instead, and the app switcher and home buttons, and makes you swipe up-right from the bottom.
I'm not a big fan of such gestures (mostly due to discoverability), but the few times I've used an Android without the navbar the gestures still felt reliable, even if I had trouble remembering them.