Does submitting to the App Store require you to provide source? If so, it seems like a compelling reason to enforce a single language to avoid the explosion in skills required for the app reviewers.
You aren't forced to use Objective-C, at least not any more than you're forced to use Java on Android. It's just the native language of the system frameworks, which you are required to use. You can literally just have a glue layer to talk to the Objective-C underpinnings and write your whole app in another language (as long as that language can compile for iPhone, obviously). The reason people don't do this is because for most people it turns out to be less productive, not more.
Otherwise, I have no idea.