The issue has been brought up repeatedly in the past, and the Mods have been pretty clear on their stance:
bigbadron:
In reply to Gluttony (msg # 1):
Only the GM controls who is part of their game. Only they can add players, and only they can remove them. We will not give players the ability to remove themselves from a game any more than we would give them the ability to add themselves to one. If you want access, or to end your access, you need to speak to the GM.
Personally, as a GM myself, I would hate for players to either "hissy-quit" on their own or just passive-aggressively remove themselves from my games. You want out? No problem. I won't stop you. I don't understand GMs who won't remove the player, unless they don't know how without deleting the characters, too.