Here's one reason why being early is sometimes a great thing: We hardly seem to install any apps on our smartphones anymore (and installation is just a prerequisite for usage). Some 65% of smartphone owners do not download and install any app in any given month. So when you think you'd have a 100 million people market on Android or iOS, it is actually 35 million.
On top of that, apps seem to become even more than ever before a short tail business. Unbelievable 42% of our whole app time (on average) is spent on the single most used app on every smartphone (in my case, Facebook). Not the most promising time to start an app business, one might think. But because of still growing smartphone penetration, the overall number of downloads is still far from declining. So it just gets harder, but remains promising to make business with apps.