Peter

I think the key point for me is that "four wives" describes a cause (people are allowed to do that, and do so), and "no wives" describes an effect (therefore lots of men end up without any wives). The latter is vague enough that it doesn't immediately tell you what cause goes with the effect – if somebody said it to me and I had no prior knowledge of conditions in country A, I'd have to get them to explain further – whereas the former makes it reasonably possible to predict the consequence of many unmarried men (assuming no unusual sex ratio) and is therefore more informative.