Regarding ESD diode's architecture
I'm not sure you are comparing apples with apples on this. The RS485 device is undoubtedly more powerful and clamps to a lower voltage than the USB device: -


SM712 clamp voltage at 5A = +20V and -10V (reverse) 
PGB1 clamps at 150V from an 8kV contact discharge


I think I've said enough to establish you can't compare the devices electrically and therefore you can't make conclusions about the circuit symbols implying one is a significantly lower capacitance although undoubtedly the USB device is lower capacitance by a long way.

As far as I'm concerned both symbols are electrically the same and, as usual, the detail is in the small print on the data sheet.