Backbone save success never fires

backbone_save_success

//This is my 'Save' handler in a view...
        saveRequested: function () {
            this.model.save({
                success: function () {
                    put('saved');  <-- never gets here, even when response is 200/OK
                    this.close();
                },
                error: function () {
                    put('error');
                }
            });
        }
//----------
//this is inside backbone.js, starting at line 375, inside the model.save() function:
      var model = this;
      var success = options.success;                        <-- contains my save callback, above
      options.success = function(resp, status, xhr) {
        done = true;                                        <-- resp='OK'
        var serverAttrs = model.parse(resp, xhr);
        if (options.wait) serverAttrs = _.extend(attrs || {}, serverAttrs);
        if (!model.set(serverAttrs, options)) return false;
        if (success) success(model, resp, options);         <-- success is now undefined... but, model.attributes.success now holds my function.
        model.trigger('sync', model, resp, options);
      };

Questions-
Why is the 'success' var undefined inside the callback function?  'model' is not.

Adding the following line solves my problem, but why is it necessary?
       if (model.attributes.success) model.attributes.success(model, resp, options);