Surely you don't think that having arbitrary code placed within the IOS AppStore isn't a security risk do you? Once malicious code has been approved in the store an attacker need only find a way to break out of the sandbox, which I am sure is possible.
Reviewers check behavior, mostly not content. It's easy to hide code and activate it later. If you can break out of the sandbox, you don't need to download code to exploit that.
