My guess is that's just a matter of model year. I think the best looking version of these is the XD 500 which has been superceded by the 600. It just had the old Sugino logo of the "S" inside the crowned shield just below the crank bolts.

Caveat: I read somewhere that there is a version of these that were not cold forged. I don't remember which version though. I think I did a google search on the XD 500 cranks and found the comment somewhere in the google results.