I'd say Backbone is a library. Ember is more of a framework.
For example, create 100 todos in their demo app, then check the select all button. Notice the instance response. This is because Ember consolidate actions and executes them once at the end of the event loop. This is not possible in Backbone without basically reimplementing that functionality.
I believe this is what they mean by "ambitious," because it's designed around issues that will arise in an ambitious Backbone project.
Backbone:Sinatra as Ember:Rails for a rough analogy.
For example, create 100 todos in their demo app, then check the select all button. Notice the instance response. This is because Ember consolidate actions and executes them once at the end of the event loop. This is not possible in Backbone without basically reimplementing that functionality.
I believe this is what they mean by "ambitious," because it's designed around issues that will arise in an ambitious Backbone project.
Backbone:Sinatra as Ember:Rails for a rough analogy.