[QUOTE]You seem to believe that any measure that improves (no matter how slightly) safety ought to be implemented (no matter how expensive) - forgive me if I've misunderstood,/QUOTE]
You have misunderstood, but i do forgive you.
3 greens summarized it well;
airline management uses (sophisticated) cost benefit techniques to decide what is safe enough .... There will always be a trade off in calculating acceptable safety ... pax understand this and don't like the 'safety is our priority' spin.