I think you are forgetting that Google doesn't sell its OS. The point of Android is to enable more eyeballs to their products since eyeballs = ad dollars. So Google will do whatever they can to get users on the Google platform (which is exactly why Google+ is great on iOS).
Maps has a huge local revenue opportunity for Google. It has user intent, most of the searches are commercial, you know the user's tastes and hangouts (through past searches), and the user is addressable (since they are close to the item of interest). This means high CPC rates (or equivalent) if you can deliver a real ad product. Thus, I'd bet pretty strongly that a maps product will be coming to iOS since Google would hate to risk losing those valuable eyeballs.