There is a technical difference because the WD switch is a “multilevel switch” and can use those command sets while the WS is a “switch binary” which only uses on/off or the central scene number.
That said, homeseer has implemented this in an unusual way. They actually define the dimmer switch as two different devices, one that handles central scene commands and one that is the regular multi level switch. I’m not sure if this distinction was implemented in the SmartThings device type handlers.
In Any case, here’s the tap behavior:
The dimmer switch can receive a set level command. The binary switch cannot.
If you press and hold the binary switch for two seconds, a central scene number is sent to the hub. Holding longer won’t make any difference.
If you press and hold the dimmer switch, it will locally change the dimming level based on how long you hold the switch. I don’t know what happens to the status at the hub, if it will show the change in dim level or not.
So the two switches do have somewhat different behaviors for the press and hold. That’s the distinction between a multilevel switch and a switch binary in Z wave.