constructor - CodeIgniter

A constructor is just like any other method.  It only differs in that it is called once automatically when an object is instantiated from the class.  

In the general sense, calling parent::__construct() is just calling a function (method) to get some piece of work done.  Different programming objectives may need different approaches.  If the child class needs the parent's constructor to run before it can do its work, calling the parent constructor makes sense.  If this is not needed (for example, the child simply adds some static functionality) then there is no reason to call the "upstream" constructors or other methods.

If so, why is the constructor in news_model.php not using parent::__construct?
 As for my knowledge it is implemented to limit such idea from model constructor where controller does.   I agree with  @Marco Gasi comments