I guess this is the result of Apple finally allowing custom keyboards[1]. I've heard people say that you can make more money developing an app for iOS instead of Android and the fact that a simple app like this typewriter emulator - which would have been possible for years on Android - could sell so much reenforces that notion in my mind.

I suppose the success could just be due to the fact that it's being endorsed by a celebrity like Tom Hanks?

[1]https://developer.apple.com/library/prerelease/ios/documenta...