Chris, what clients do is not necessarily what they should do. Buying most of your suits in a particular weight of cloth is sheer idiocy, regardless of how many people do it--unless you live where the weather doesn't change. Assuming one experiences both hot and cool seasons, and he is not some sort of biological miracle whose body temperature adjusts itself, he will need suits in different weight cloths. However, even more importantly, looking good in classic men's dress means looking seasonally appropriate. So what if you feel comfortable wearing a flannel suit in 90 degree weather? You'll look terrible.