I don't have a background in biology, Pgardn (though I did well in it at school), but from working at the zoo, one picks up an awful lot.
Right, my examples were that humans aren't alone in having differing lengths of hair on their bodies- I agree about the function of the horse's tail, etc.
I still think there may be something to hair as a sexual attractor- women's hair is thickest around age 15 or 16- it's all downhill from there.
Here's more on body hair vs. head hair, from Wikipedia:
Body hair
Historically, several ideas have been advanced to describe the reduction of human body hair. All were faced with the same problem that there is no fossil record of human hair to back up the conjectures nor to determine exactly when the feature evolved. Savanna theory suggests that nature selected humans for shorter and thinner body hair as part of a set of adaptations to the warm plains of the savanna, including bipedal locomotion and an upright posture. There are several problems with this theory, not least of which is that cursorial hunting is used by other animals that do not show any thinning of hair. Another theory for the thin body hair on humans proposes that Fisherian runaway sexual selection played a role here (as well as in the selection of long head hair). Possibly this occurred in conjunction with neoteny, with the more juvenile appearing females being selected by males as more desirable; see types of hair and vellus hair. The aquatic ape hypothesis posits that sparsity of hair is an adaptation to an aquatic environment, but it has little support amongst scientists and very few aquatic mammals are, in fact, hairless.
In reality, there may be little to explain. Humans, like all primates, are part of a trend toward sparser hair in larger animals; the density of human hair follicles on the skin is actually about what one would expect for an animal of our size[1]. The outstanding question is why so much of human hair is short, underpigmented vellus hair rather than terminal hair.
And the whole entry:
http://en.wikipedia.org/wiki/Hair#Growth