Without diving too deep into rendering theory - there are two kinds of renderers, one kind is good at fine displacements, the other is good at raytracing. Both kinds can do what the other can, but they don't excel at it. It's a trade-off - there's no renderer that is fast in both disciplines, it's either one or the other. Renderers that are great at displacements but slow at raytracing are REYES renderers like Pixar's Photorealistic RenderMan, 3Delight or FireFly/Tempest. Renderers that are fast at raytracing but bad at fine displacements are for example Mental Ray, Cinema 4D or Final Render. Bottom line: Poser 5 can do raytracing, but it's not its favorite discipline. In exchange, its displacements or depth of field put C4D to shame.