To hire reporters you need $. To get $ in the digital age, you really should have some control of the distribution of your content. Therefore, an app makes sense, especially at NPRs scale.
NPR has had INTENSE control of their content since the 1970s. They don't need an app for that. They also have staggering amounts of donations and endowment funds. They may, sadly, have more money than they know what to do with.
