They had this for a long long time but then some time back they divided the skillset into PvP and PvE. It meant that any balancing done for PvP would only be reflected in a PvP area and in PvE areas they behaved like normal PvE skills. This allowed them to tweak skillsets as and when then liked for the differing environments. It was one of things people complained a lot about and although they did not have to do it they went ahead and implemented it.