Upon further investigation, it looks as if I may have found the only effective use conditions for the pointlight in preview.  My image looks OK because while the surface casting the shadow is complex, the surfaces receiving the shadow are both flat.  I added a point light to a more complex scene containing actual props and the result are not so good...  That tells me Poser has no trouble creating a shadow volume from a point light, but then is not so good at determining what parts of other objects are within the shadow.