I may be misremembering but my understanding was that Apple disallowed other rendering engines not primarily for security reasons (although I'm sure they're a f

I may be misremembering but my understanding was that Apple disallowed other rendering engines not primarily for security reasons (although I'm sure they're a factor), but for performance and, by proxy, battery life. It's not dissimilar to the argument against Flash: yes it was insecure and unstable, but mostly it was a performance hog and a battery drain, which isn't great on mobile devices with limited battery life.