I realise that non-system hair and skin is far more popular because both can be made to look realistic, but there are good reasons not to use them.
Fast change of clothes is easier using REPLACE ALL when one's hair doesn't dissappear along with the old clothes. Prim hair generally requires the AV to also use a "bald cap" to be worn, but if the hair's detatched for any reason one is left bald. Most of these characters were constructed before Viewer2, so there were no links to inventory items. Laurel's original shape and hair is based on DARIA MORGENDORFFER as per image below. There was no need to make that any more realistic, because as animated on the MTV cartoon series, her details are pretty basic.
I also found in practicle terms, using system hair meant that I had another attachment point to use, for hats, et cetera.
It's funny though how many folk think that using system hair is through ignorance rather than choice. I met a 7' tall AV the other week who insisted on sending me LMs to "better fashion" places! My AVs do dress up and use prim hair, but it's easier not to do that when posing (excpt for Marble, who's hair has been borrowed from a Sweeny Todd AV when he's human). :)