If Apple is reluctant to approve a Google Maps app, and Google claims that they have the app ready and waiting but Apple won't approve it, customers will be pissed. This would put even more pressure on Apple.
Google could absolutely prove anti-competitiveness of the App store, by simply releasing the app that existed on iOS5. If it's the exact same app, with no new features, Google could ask the question why it was good enough for iOS5, but not iOS6. If Apple is restricting its availability simply because Apple has their own maps app, it could definitely be shown as being anti-competitive, and if the DOJ or FTC started to investigate this, Apple would be in heaps of trouble. Apple would be stupid to risk getting a decision forced down their throats by the government, a la Microsoft.
The one thing that Google may be doing is waiting until after Thanksgiving or Christmas in order to release their new App. They might be letting the bad press over Maps could hurt sales of iPhone 5, and then releasing an app after January.