Anyone who throws a real-life example into the works is missing the point entirely.
This is not real life, its a game, in which usernames are essential to prevent confusion between characters.
Confusion between characters can lead to characters and reputations getting damaged. Suddenly my game-time (already filled with random noobs asking me in PM where the bathroom is) gets further packed with PMs from people saying "are you Jose_Carlos lol?"
It wouldnt be nearly so much of an irritant if one player in question (Jose_Carlos) was not now a bomber-flying Corsair with an RP style remarkably similar to my own....