Its probably not needed. I don't see any real benefit other than space, but I don't think that's too much of a problem for theymos. I guess it does skew the forum statistics a little bit, but I don't think that justifies it. I don't really see too many benefits of doing it.

Maybe, later down the line things will change, and theymos will start pruning old accounts, but I think I remember this being discussed before, and it was ruled out for a few reasons. I can't seem to find that thread though.