In my circles, there is a pretty clear pattern about this – the older the generation, the more chance of calling with a title. In my family, my fathers siblings are much older than my mothers (my father is youngest, mother is second), and we call all my maternal uncles by first name but paternal by Uncle/Aunt title. It is simply got to do with how casual the relationship is, and the younger they are the more casual (and automatically less respectful) the relationship is.
