Drupal 7: Using AJAX with menu callbacks

I am confused why this is considered an AJAX request, it looks no different from a normal 'hook_menu()' and what usually entails it's callbacks and corresponding arguments. So why is this considered an AJAX request, and other callbacks aren't -- or, are all callbacks in hook_menu() considered 'AJAX requests'?

Let's look at a typical AJAX menu callback use case. Suppose we want a module that allows users to add or delete items from a list via a dynamic AJAX callback. The module might set up something like the following:

-Drupal Module Development, pg. 236

Also, this example seems rather ugly. You would goto this long url address:

http://yoursite.com/example-ajax/%item/add/%user/[whatever]

to simply get a link that says, "add to my list", if you have the "permissions" to do so.

1. Our hook looks like the following:

function example_menu() {
  $items = array();
  $items['example-ajax/%item/add/%user/%'] = array (
    'title' => 'Example AJAX add to list',
    'page callback' => 'example_ajax_add',
    'page_arguments' => array(1, 3),
    'access callback' => 'example_access_ajax_add',
    'access arguments' => array(3, 4),
    'type' => MENU_CALLBACK,
  );
  return $items;
}

2. This allows us to pass a Drupal authentication token to our access callback. To make this work, we modify our link creation code to include a token:

if ($user->uid > 0) {
  $output = l(t('Add to my list'), 'example-ajax/', . $item->id . '/add/' . $user->uid . '/' drupal_get_toekn($user->uid);
  return $output;
}

3. This will generate a link similar to:

<a href='/example-ajax/3/add/10/c342324924cd2342'>Add to my list</a>

4. Then in our access callback, we check the token string in addition to the user:

function example_access_ajax_add($account, $token = null) {
  global $user;
// check the validity of the user account.
  if ($account ->uid == 0 || $account->uid != $user->uid) {
    return false;
  }
// check the validity of the callback token
  if (empty($token) || !drupal_valid_token($token, $account->uid)) {
    return false;
  }
  return true;
}