Sometimes I think that schools need to take thing son a case by case basis.
We had a child who had life threatening reactions to strawberries and seafood at school for the last couple of years so the school had a policy where those foods weren't allowed but now they have left so it's tuna sandwiches and strawberries all round. The nut kid is still there (although no-one knows who s/he is) so we continue with the nut free policy. We're a small school so the policy can be flexible but in a large school I guess there is much less room for flexibility.
A life threatening or fatal reaction isn't just traumatic for the child who reacts. It distresses teachers and fellow students too. By adhering to a nut free policy we save ourselves the trauma of being the person who was responsible for little Suzy being rushed off in an ambulance.