Shoulders are a pain to rig. I think I read that Shrek had 30'ish different rigged versions to make the movie. Somebody correct/expound. Anyway, in Poser we always deal with models with just one rigging implementation. If Hollywood has to rig 30'ish versions of the same model for good results then I don't feel too bad when our one version doesn't bend exactly right in every pose. I don't think there is any software that can make 'the perfect shoulder joint' that will work well for every pose, at least not with polys. I'm no daz fan, but I can't really fault them for that limitation.