Saving a default value when using entityMetaDataWrapper->save()
The default value is used for the widget form only, it won't be automatically set if you use node_save or a metadata wrapper. You see it in the form when you edit the newly created entity because there's no value for that field, and Drupal dutifully fills in the default value. It doesn't update the value of that field on the entity, just populates the form input.

You'll need to populate it manually, but you can get the right value with the field API:

$instance = field_info_instance('node', 'field_foo', 'article');
$default_value = $instance['default_value'];