Karl Saidla brainstorms about the different race distances for men and women in skiing and why these differences exist.
It might be true that these discrepencies are unfounded, and the main one I would argue is the women's 30km vs. the men's 50km. Over longer distances, women are much closer to men because of the fact of their naturally better developed free fatty acid metabolism. They can generate much more power than men through this system over the long haul and this is the reason why you see women often competitive if not better than men in ultramarathons (hundreds of km foot races). The glycogen stores in the body are not enough to be the primary fuel over a 50km, so fat needs to be tapped into as a significant energy source (along with well planned glucose fuelling). I think the time difference over a 50km between men and women would be relatively small compared to if both sexes were to race a 15km.
Men's Marathon World Record: Haile Gebreselassie - 2:03:59
Women's Marathon World Record: Paula Radcliffe - 2:15:25
Pam Reed from the states won the 135-mile Badwater Ultramarathon race down in Death Valley two years in a row (2002, 2003) against current-day super stars like Dean Karnazes (all of you skiers who may remember this article in a mag up on the Haig...). Mind you, this isn't like an xc 50k that takes you like 2 and a bit hours, the Badwater is usually won in the neighbourhood of something like 27 hours.
I think that with proper training women can regularly (and easily) crush men in the epic ultramarathons (watch out Zahab!), and that time differences could be narrowed in shorter events like the marathon.
Gawd, that sounds like an essay...