field_delete_instance in Node Example uninstall is redundant (or perhaps not commented well enough)

In node_example_uninstall(), each field defined by the module is looped over and deleted as follows:

  foreach (array_keys(node_example_installed_fields()) as $field) {
    field_delete_field($field);
  }

Then, each field instance is looped over and deleted:

$instances = field_info_instances('node', 'node_example');
  foreach ($instances as $instance_name => $instance) {
    field_delete_instance($instance);
  }

However, field_delete_field deletes not only a field (as its name might suggest) but marks "a field and its instances and data for deletion." ( http://api.drupal.org/api/function/field_delete_field/7 )
Therefore, any instances of fields defined by this module will already have been marked for deletion by field_delete_field(), and there's nothing for field_delete_instance() to do.

The exception to this would be if the node_example node type had an instance of a field defined by another module (e.g. if the user had added a field via the "Manage Fields" page at admin/structure/types/manage/node_example/fields ). In which case the instance of that field should be deleted before the example node type itself is deleted.
If this is the purpose then I think a comment to this effect would be helpful, since at the moment the code reads as if the field_delete_instance() call is necessary to delete the instances defined within the node_example module itself (which it is not).