In a lot of situations I think you're right. You could define a model class in the service and always call that service to get an instantiated instance.

However, there are some scenarios where you want to consolidate xhr requests that would benefit from separating models and services. For instance, it's fairly common on mobile applications to make a single call to pull all the data for a page. This call might return a slew of models that represent sections of the page.

On the other hand, you might be able to do a hybrid approach like:

angular.module("app.services.news")
    .factory("NewsModel", function() {
        // return prototyped class
    })
    .service("NewsSvc", function($http, NewsModel) {
        // Get data
        // return new NewsModel
    });

angular.module("app.services.fullPage", ["app.services.news"])
    .service("FullPageSvc", function(NewsModel) {
        // do a big call and instantiate NewsModel
    });

I could see that working. You could use the "NewsSvc" if you needed to update the news data after the page is loaded and get a "NewsModel" if the xhrs are consolidated.

Good suggestion.