Global growth probably doesn't matter as much if your app isn't hasn't been localized to all of those places. For example, growth of Android in a country where most people don't speak English isn't going to do much for an app written for an English audience.

If Android's growth is X times the iPhone's growth, and Android had a bigger "market share" a year ago (according to the article's chart), shouldn't iPhone's share be lower than Android's?