Here's what the documents I have say (all official Porsche documents, not some sales guy's opinion):
For 996 (I checked Carrera and Turbo S):
CPZ ($730 in US) is "thicker steering wheel"
XPA ($1,280 in US) is:
"3 spoke steering wheel--interior leather
Finished in leather in interior color: steering wheel rim with cross stitched seam, airbag module, hub cover, includes airbag"
For 997, option XPA ($1,050 in US) is "thicker 3 spoke sports steering wheel in smooth leather"
This is how it's listed in the 997 order guides.
In the vehicle distribution bulletin (which PCNA updates periodically to communicate option availability to the dealers) it was stated in early October that a bunch of options that they listed--including option XPA--were unavailable for ordering for 997, even though they were listed in the order guides, and PCNA would communicate when they would be available for ordering. Then in mid November, it was communicated that several options--including XPA--were released and now available for ordering on 997 models. The confusion seem to be that the vehicle distribution bulletin describes XPA for the 997 as "3 spoke steering wheel--interior leather" even though the 997 order guides describe it as "thicker 3 spoke sports steering wheel in smooth leather."
My guess (but just that!!) is that XPA for the 997 is the "thicker 3 spoke sports steering wheel in smooth leather" and that whoever updates the vehicle distribution bulletin incorrectly picked up the XPA description from the 996. I can't imagine Porsche lowering the price from $1,280 (996) to $1,050 (997) if XPA is the same option for both models.
That's about as clear as mud...