This tweet thread is unnecessarily confusing the two. How does restricting browser engine to webkit decide what browser engines they use?
By: 1. Eliminating browsers ability to differentiate itself 2. Forcing additional costs on the browser vendors to have to develop a second browser specifically for iOS 3. By reserving functionality exclusively for Safari 4. By eroding third party browsers market share by self-preferencing Safari (default install, couldn't set another default browser until recently etc etc)