Dmitry Nekrasovski has some thought-provoking ‘design principles’ for converting iPhone apps to Android. He concludes that user experience differences between Android and iOS are only noticed by expert Android users.
This implies it’s possible to keep much of the UI the same and only change a small sub-set (e.g. parts of the UI the Android buttons make obsolete). I suppose it’s an interesting, alternative, pragmatic approach for some types of projects on a lower budget.