angular dot notation better explanation

I was looking for a solution about polling data using AngularJS and I found here at stackoverflow.

In this solution (shown bellow) it is used a javascript object to return the response (data.response) and if I try to replace that data object for a simple javascript array it doesn't work, I would like to know exactly why I need to go with dot notation and why a single array doesn't work? (It would be great links or explanation with examples)

app.factory('Poller', function($http, $timeout) {
  var data = { response: {}, calls: 0 };
  var poller = function() {
    $http.get('data.json').then(function(r) {
      data.response = r.data;
      data.calls++;
      $timeout(poller, 1000);
    });      
  };
  poller();

  return {
    data: data
  };
});

Trying to summarize my goal (what I want to really understand): where is var data = { response: {}, calls: 0 }; could be var data = {}; and then the response.data would be setted directly to data data = r.data and return {data: data};, why do I need to rely on dot notation?

Let's say if we change the factory in this way:

app.factory('Poller', function($http, $timeout) {
  var d = {};
  var poller = function() {
    $http.get('data.json').then(function(r) {
      d = r.data;
      $timeout(poller, 1000);
    });
  };
  poller();

  return d;
});

In the controller, the statement $scope.data = Poller; assign d object to $scope.data, so the object relationship is like this after the initialization

$scope.data -> d -> r.data

When poller() is called again in 1 sec, d is replaced with an new object, so the object relationship will be

$scope.data -> d* -> r.data (d* is a new object)

so the angularjs's data binding will be broken since there is no way to trace to the r.data since d* is a brand new object with different prototype.

With dot notation, after the initialization the object relationship never changes since the periodic calls to poll() doesn't create new object d but it just keeping updating the response field with new r.data object.

$scope.data -> d.response -> r.data