Most of the frameworks available provides at least one of this things:
- Configurable Widgets
- Navigator abstraction (DOM Helpers, etc.)
- Language Improvement
All of this is very useful, but almost none of these frameworks are designed to help making a good clientside app.
When you work on the server side, you have plenty of frameworks to help you designing your application with a good structure, separating the view, the controller, the model, the front, the middle, and the back of your application. This ables you to have a more readable code, good practices, flexibility and efficiency in your work.
Archetype is designed to fill these gaps on the clientside, in order for you to work in a good manner, with a lot of reusability.