Clint,
You are right, there is no difference if we set the layer Order properly.
The reason we put the label layer and symbol layer to different overlays, is that in that way, when adding label layers, we only need to consider the order among labels. Similarly, when adding symbol layers, we only need to consider the order among symbol layers. That has the same results but make our developing work easier. :)
Also, I think developers can follow the same pattern when creating a complicated map, that little trick improves the developing efficiency greatly sometime.
Ben