I agree, Chaotica, that women are, overall, more adversely affected by the decision to have a family because of the biological differences. I guess that where we'd differ is that I'd say that the biological differences are relevant for such a (relatively) short period that they disappear into the wash when looking at it over a whole career. (Maybe I'm being overly optimistic though, or underestimating how easy it is to fall off the career ladder...)
And I agree fully that women are discriminated against by the assumption, commonly held by employers, that it is them and not their male partners who will take the brunt of the childcare (whether or not they currently have children!) It's partly for this reason that I get antsy when I think I see issues for "women" and "parents" being treated as the same thing. I think it's damaging for everybody if the current cultural norms are perpetuated as if they are fixed in stone.
This links to Karmakameleon's point - I know it's the case at the moment that men are more likely not to be primary carer in a couple, but I would see this as the result of choices that individual couples make. The operation of our home lives is not an immutable fact - I guess this is probably where I start to agree with Hakim that women (and presumably men) make choices. So, I'm not saying that long hours cultures don't disproportionately disadvantage women, given the other choices that they and their partners have made in life - but I'm arguing that this isn't sexism but about choices that the sexes have historically made differently.
So it is a gender issue, yes, but, to me, it's not about workplace discrimination, but rather it's about the negotiations that happen in individual relationships. I think this is a really important distinction - it certainly has significant implications for, say, what I'd see as appropriate public policy.
The other reason I get exercised about this is that I think that there's still an awful lot of what is to me "true" sexism around - I worry that if we bundle e.g. long hours cultures in as well, then it starts to look like special pleading because we want more than is possible in life and it weakens the case against the Daily Mail "feminists have always been wrong-headed idiots" type argument.
(Sorry, long again - am trying to work out what I think about this as I go.)