They can replace some native apps. With Meteor, you can now use the same basic building blocks to build your web app, iOS app, and Android app. Maybe you won't

They can replace some native apps. With Meteor, you can now use the same basic building blocks to build your web app, iOS app, and Android app. Maybe you won't reach the same quality on iOS and Android as you would with native apps, but for smaller teams this can be a huge time saver, especially in the early stages of a project. So in a lot of cases it's not so much "web app" vs "native app", as "web app" vs "no app".