No, I think you take it just right. My lists, with the exception of the short list which is my personal list, were all created by request only. I don't get people dropping in large numbers but do get the occasional reqest to be pulled. Everyone was warned it was high volume. The list seems to rest consistantly at about 200 names. The GGG list is also about that size. It's not one of the larger lists on this forum but propably contains some of the most dedicated as all are activists in these areas.
My list grows very slowly, and it's not all that large, just 135 names at the moment. The subset of my list that I use mostly for cosmology and physics threads is maybe half that size. So the numbers are small, but the quality is awesome! Of course, the evolution threads aren't for everyone because they sometimes become quarrelsome, and my list is limited to the evolution side of the issue. I assume the creationists have their own ping list, but I don't know who runs it. I've seen no evidence of such a ping list being used in the evolution threads. My guess is that the creationists notify one another mostly by freepmail.