I am talking about apps, not games :) . Of course for games you want to use a cross platform approach, for example with unity. They are a very specific case though. For games : -you probably don't want to use the platform's UI framework (unless you game is extremely simple and even in that case it is probably not the best choice for crossplatform). -the platform specific layer is pretty thin. Google Play Games/Apple Game Center. Share achievements, tweet game events and that's it.

None of this applies to regular app though.