I'm not 100% sure, but I think most of the jailbrake exploits use some form of safari or webkit bug to modify the system. Apple is very aware that the browser i

I'm not 100% sure, but I think most of the jailbrake exploits use some form of safari or webkit bug to modify the system. Apple is very aware that the browser is the most targeted point in the OS. By the nature of modern JS interpreters they would need some kind of low (or lower) level access to the CPU to be competitive and that will open a new vector, maybe multiple, for attack that Apple would not be able to control. I think their decision is about a lot of things including the App Store, but security is certainly one.