kozaburo-sama found same thing: bake in specular of poser hair, going back to P4. poser can simulate specular on hair with direct or indirect lite, but I'm not seeing any fresnel shaders for hair yet.  bill added schlick approx. in first shader posted above by anthan, and that's about it.

not certain about this, but some of 'em may still be turning off raytracing for hair, to speed it up.