1) If the system is small and you just need to show the contents of a database, you can stick to the MVC used by struts, or others... wich mean that the Model object is the database encapsulation.
True, most MVC-for-the-web frameworks assume most of the model is implemented using an object-relational system, but struts does not mandate that. In fact, struts (like most other MVC systems I've seen) doesn't even have a built-in oo-relational library, although it does make some assumptions about your model's API. In short, you are typically free to design your model classes in any way you want (but see below).
The main key to MVC is a magic keyword named: "event". The key is... When the model is changed, it notifies the changes, so if the model is changed by the Controller (I mean, loading the data) the UI is updated, and if the UI changes the Model, the controller can be notified and do some extra calculation (I mean, sum the values and set the total value in the model and the UI will be notified).
Yes, and this is exactly where most web-MVC systems do things very differently compared to traditional GUI MVC systems, which tend to use Observer pattern or callbacks to link Model and View. First off, since the web mostly works with HTML pages that can only be updated via request/response actions (I'm ignoring flash), you can't really have a model update the view's output directly. Also, there are so many possible views that updating them all would be very inefficient.
What tends to happen is that for each request, after the model has been updated, the view just queries the relevant model objects and generates new HTML/XML/whatever output.
The exception to this is caching; cache-invalidation can sometimes handled by observing the model (however, in this case the observer responsible for clearing the cache is usually not the view or controller).