All the companies I have ever worked for did a head count - is there an airline that doesn't??
As has been said previously though to get to the a/c two checks on boarding pass have failed.
I have never envied the cabin crew's job doing a headcount and being human I wouldn't be surprised by the odd error now and again.
But as long as the crew had pots of yoghurt or a can of Coke confiscated by security we have nothing to worry about.....