I can think of some urls with underscores that are still sought after (Emotion ones {o_o, T_T}, words paired with only an underscore if the word is that sought after as a url {love_, love, _love}), ﹠ I think that it isn't too laborious of a task to just edit your urls once a year, so the claim rules don't place much stress on people who are uninterested in interacting with the system in the first place.