For your convenience, here is the net of it. With MVC, the model is
thick with business rules and glue code to a data access layer. The
view has lots of dependencies on the model. The controller is usually
a framework component driven by some kind of configuration, usually
XML based. With MVP, the model is lightweight POJOs. The view is
mockable. It is the presenter that is heavy with glue code and
business rules. The thinking here is that MVP is more suited for TDD
than MVC.
Another notable feature of MVP in GWT apps is the use of an event bus
instead of hard coded event handler dependencies. Typically, that
event bus is implemented as either the HandlerManager from GWT itself
or the PropertyChangeSupport class from the GWTx library.