I don't agree with it, and am HIGHLY against it, but one thing came to mind when I was thinking about it...
There might actually be less people shouting swears in the vocal chat than in the written stuff. Think about it, a majority of them are probably idiot 12 year olds you get themselves a case of keyboard courage, and writing these things when they probably can't in real life. So they wouldn't risk saying them through the vocal chat because then their parents can hear them.
But it wouldn't stop it, and unfortuantly there would then be the poor souls who get told not to play by their parents because of the swearing they would now be able to HEAR being shouted.