Prevention by Investigation vs AF 447 Blame Game

If prevention of a mishap similar to the one being investigated is not the purpose of the safety mishap or incident investigation, then what is the purpose of the investigation?
If the purpose is to level blame, for one party to escape blame, to shift blame to someone else, to share blame with other parties, well then that investigation is a lawyers investigation, a damages investigation, an insurance investigation- but it is not a safety investigation. Remember that a safety investigation is purposefully tasked with determining the cause so that a prevention process can be developed to keep the event from reoccurring.
Where has the AF 447 investigation taken us in terms of prevention?
Is the investigation really living up to its purpose?