The environment mapping technique was introduced to enhance an object's reflections without tracing the secondary rays.  Instead of intersecting secondary rays with objects, an environment map is computed from the normal, and angle of incidence.  If this were the case here, then increasing bounces beyond a certain point would initiate the CEM, and render time wouldn't increase exponentially beyond a certain point either.

So wouldn't this mean Poser should render reflections a lot faster than it does, if it were actually using this reflection "cheat"?