There are some other reasons related to user experience. We can do a bit more in an app than what we can do in a browser e.g. push notifications for new titles and more control over UI. Also, I feel people like apps because people like to put things in "buckets" mentally.
But you are right - if/when we get some traction, we will provide a full-fledged platform on the Web also. People can choose where they want to read. Thanks for your thoughts.