It would appear Apple and Google could have kept the Maps app powered by Google for another year, at least according to sources who spoke to The Verge. The decision was made before WWDC this year, and caught Google unaware (according to sources), which is why we still don't have a Google Maps app.
According to the report, Apple felt Google's offering was lagging behind. Plus there's the contractual limitation of turn-by-turn directions (available on Android), as well as the added drama of Google requesting more branding and the inclusion of Latitude.
Despite having a year left on the established app, however, Apple decided to go it alone. The Verge, and we here at TUAW, are already seeing progress on data points which were missing or incorrect, but mapping the planet and adding relevant data for businesses and such is -- quite literally -- no small matter.