Rating systems are subjective regardless of what entity is pushing them. At least an outwardly private company isn't going to pretend they're unbiased like a government could and would.
It would be pretty obvious bullshit if, say, EA was in charge and every other game company mysteriously received shit ratings. Not so much when the governing authority can make back room deals while pretending to have the public interest in mind.
Caveat, I am American, so dealing with our political system is probably coloring my view. Shit brown.