Another example - I can make Viber the default handler for all messaging, both sms and Viber messages.

I can make Firefox my default browser for everything and it's not just a wrapper around webkit.

I can share to pocket from almost any app, not just those that explicitly code for it.

When I want to attach a photo to an email I can choose from any app on the phone that provides images, not just those that the app developer found time to support.