I suspect the biggest part of the "improvement" in the Hair Room in P6 is more realistic expectations. The Hair Room works, in P5 and P6, if you keep the models low-res.

I checked the skullcaps for P5 hair, and they were over 1,000 polys. The skullcaps for the P6 hair are only about 100 polys. That's just what people like Kirwyn and Softriver have been saying: the standard P5 dynamic hair is way too high-res to work properly.