The rules were in affect long before the TSA took over. It was an FAA rule in conjuction with the airlines that a % of passenger have additional screening. When the TSA took over they adopted the FAA rules. It was easier to do this than make up new rule in the time span they had. The airlines can deselect any passenger from additional screening. The problem is most agents do not have the knowledge to do it and it requires the supervisor ok. Most airlines will tell you they can't do it but if you complain enough they will.