I think Android as an OS has a major effect here, because its Intents system codifies that 'starting point for a task' concept. If I want to carry out a particu

I think Android as an OS has a major effect here, because its Intents system codifies that 'starting point for a task' concept. If I want to carry out a particular operation on some data, all of the apps capable of handling it can inform the OS that they are available as options, and I get a menu to select which app I want to use for the task. What you want, as an app developer, is to have your users become confident enough in your app to check the "set as default" option in that app choice menu. This is kind of the equivalent of the fight over 'file associations' in Windows.