An author here. What drop-downs are you referring to? We are a server-side framework (GWT = client-side). That means there is no need to implement a client-server protocol to access server-side resources, which, as application complexity increases, is a huge benefit.

JWt is also the web framework with best support for refactoring (no string-based bindings) and best support for OO design (you can specialize widgets easily).

A JWt application does not rely on JavaScript (unlike GWT) and can be properly indexed by a search engine (unlike GWT). That makes it more general purpose.