Many of the features they offer for Google Maps on Android haven't been implemented for iOS (turn by turn navigation, interior views, floor plans, 3D models, etc.)
Google is already polluting the iOS Maps app with sponsored listings, degrading the user experience severely. I doubt that a separate Google Maps app for iOS will be any better.
When I mention this I receive the response "Google will just make their own iOS app." I'm skeptical given the history of their Gmail app.
When I wrote about a ‘good Google Maps app for iOS’ I meant one that has feature parity with Google Maps on Android and contains no ads. Up until two years a go, the Maps app on iOS was such an app.
Google and Apple are in a fight, but Google has little to do with the map app that comes on every iOS device. Much like how they came out with Chrome for iOS (despite Apple's crazy limitations) I expect a very nice Maps app as well. One that they control and are allowed to update.
http://www.flickr.com/photos/timmygunz/7161691115/
It's also clear that Apple would've loved to implement features like turn-by-turn navigation in the Maps app, but Google wouldn't let them. With iOS 6, Apple says goodbye to Google Maps and voilà: turn-by-turn navigation.