"""If women's natural imperative is to raise children and nurture them, why is Penelope Trunk running a start-up?"""
1) She doesn't, as a comment below states.
2) I fail to see how your question makes any sense.
Tendency/Preference etc is not Absolute Law.
For example, a human's natural instinct is survival, yet there are still people willing to sacrifice their lives for others in danger, etc.
(I always hate it when someone takes some statistical observation and thinks it's very smart to point out that there are exceptions --or even worse, uses them to "prove" the statistical observation doesn't hold. Happens all the time in pedantic-land).
"""I really thought that this kind of overly-simplistic "men do X, women do Y" was in the past now, but of course such things never die."""
Overly simplistic? Just because there are counter-examples, and complex cases, doesn't mean that the generalization is overly simplistic.
To make sense of the world you have to generalize, that is not to give equal importance to a multitude of fringe cases.
"""I hope you see the irony in thinking that there is nothing stopping women from running startups, but they shouldn't want to, as women want to stay at home and look after the children."""
Nobody said "shouldn't", she said "wouldn't".
And, statistically speaking, most don't. Do you see equally as many women founders? Or do you think you can attribute that to some mysterious general sexist attitude that prevents them?