The "in-app browser" is Safari, not their own rendering engine (Which is explicitly disallowed.) The difference between in-app safari and external...is that the

The "in-app browser" is Safari, not their own rendering engine (Which is explicitly disallowed.) The difference between in-app safari and external...is that the app can get callbacks for every link tapped within the in-app browser, and the app itself can inject javascript into each web page it loads, which essentially means unlimited perfect tracking for social networks (Since the user is already logged in to the app.) This sounds bad...but the integrated webview is necessary for things like Cordova/Ionic/React Native/etc to exist on the platform. It's also a byproduct of iOS's pre-multitasking days where launching out to Safari was a big context change, vs now where you can just swipe back to the app you were in.