Just looking at things from a story point, if we have the same player names as forum names, then every single time that player plays they play the same person.
E.G, Gl1tch from war 1 says hello to Gl1tch from war 5. Plus, if characters who do well remain in the environment, there will be dopplegangers running around.
At the same time, forum/player names get pretty confusing, and most of the time forum names are used anyway.