Steem don't need mobile app.
Modern frameworks like React, Angular 2, Ember etc can deliver really good mobile experiences in the browser.
Today I've used steemit on my iPhone 5s and it was great and it will be better over time.
With modern web applications we could go very far.
Its close. Can web apps provide compelling experience , yes. Can provide a full experience, no. Issues - 1. Lack of native push notification 2. No easy/convenient way to add to home screen for average user (possible but not mainstream.) 3. Lack of consistent way to upload photos / videos (this has gotten better though and might even be the same - I haven't used any web apps lately that required). 4. Sure they want to add chat at some point which tends to require the first 3 to do fully (http://www.lukew.com/ff/entry.asp?1696).
I do agree Steemit should be able to go quite a ways before needed an app.