The key here is intention. While of course it's quite possible for images to be reproduced in one way or another, the fact that they must be reproduced, and not simply 'shared' or 're-*ed,' changes the user's relation to the app.

I think this gets to the tone of the article, as communicating this way implies a level of trust and/or intimacy usually reserved for analog methods.

Snapchat is brilliant in this regard. I think we're going to see a lot more communication platforms built on limitations rather than sprawling features.