I think I may have found my answer...
The WS12A and WS14A are regular X10 part numbers, the XPD3 and XPSS are the X10 Pro counter-part numbers.
SO...
WS12A = XPD3 (decorator, dimmer, single/3-way operation)
WS13A = XPS3 (decorator, non-dimming, single/3-way operation)
WS14A = XPSS (decorator, slave/companion)
Am I correct now?