I think the MO example does show something…there just are not that many 8 year olds that weight over 125 pounds. Are there some? Sure, there are exceptions to every rule. And even with some of the suggestion on this post there would be exceptions. If we move it to 150…what about the kid that weighs 160 (and so on)???

My son is 8U 110, and even at that weight there are usually not more than a couple kids his size. So I can see why people would assume there isn't enough participants to warrant additional groups.