[saurik]

The Android back button is a concept that doesn't really exist on iOS (except as an informal protocol with inconsistent UI cobbled together between a handful of apps, many of which were written by Google...): swiping left is more like clicking "parent folder" than "back"; think what happens in a file system or web browser when you click a symlink/shortcut or hyperlink: that is closer to the Activity/Intent model of Android, and back serves the universal purpose of not just going "up" the folder/breadcrumb trail inside of an application and an actual "back" in Safari, but also allows for global "back" during tasks like returning to the web browser from an app you might have entered, or back to Yelp from the Maps app, or back to YouTube from a web browser.