Help me clarify this really unclear diagram?
The way they are asking you to connect the VSS and COM pins is to avoid load ground currents infiltrating the logic ground connection. 

COM is a floating output and naturally should directly connect to H bridge 0V (shown as a large rounded rectangle). VSS is fed from the logic 0V directly. The logic 0V is, in turn, fed from the rectifier return point. This prevents H bridge currents flowing thru the more sensitive logic 0V and corrupting the logic ground with noise.