There has been abusive pm-ing in the past and posting abuse that lead to having these timers invoked. Not only does it help stop spamming it gives the sender time to cool off if a flame war has broke out. As far as banning an abusive pm sender, the mods can not see your pm's. It's private mail so to speak. If you make public what you have received then you are in the soup also. If you get an abusive pm then forward it to a mod. DO NOT post it in the open.
Some times we have to do some thing that is a little bit of a pain in the kazootenblatts to some to server the greater whole. Like Spock said> The needs of the many outweigh the needs of the few, or the one.