Poser's renderer is a REYES renderer, not "sub D" (Catmull-Clark subdivision).  They don't behave the same way, although with high-poly models the results can look similar.  The differences become very obvious with low-poly models (like a 6-side cube).  More info:

http://en.wikipedia.org/wiki/Reyes_rendering
http://en.wikipedia.org/wiki/Catmull-clark_subdivision

My Freebies