This is supposed to be an introductory tutorial on Backbone. That should not be a concern. Second, the author makes the claim that Backbone is an MVC and makes things simpler and yet violates that. His way you literally have to go through the view, the collection, the model, a trigger, and back to the view to select a new image. WTF?

It simply is a matter of concerns. Ideally, your model should represent the state of your application, it doesn't matter if an event needs to travel one or more layers in order for that to happen. Views may very well be a representation of the model. Although the MV* stack is packed with examples (MVC, MVP, MVVM), here is one example ('Passive View'): http://martinfowler.com/eaaDev/PassiveScreen.html