I think the thing with the US is you are either in or you are out. You can't go part time - pretty much unheard of, no right to ask, you'd probably lose your health insurance and your paid vacation. You take maternity leave for a very short period (and as an interesting aside, maybe this contributes to more people returning, because you don't change pace and your whole leave is spent planning your return).
What I think that means is that those who stick it out compete on a far more equal playing field (though I am under no illusions who bears the burden of nursery pick up time).
But, and it's a big but, I'd be interested to know what their attrition levels are overall - do more women leave the work force with no compromise option.
And another big but, I'm not sure I'd want to live in a society that treated people that way. I think that, long term, the solution is moving to better work life balance, not forcing everyone to hand over every waking hour and their soul to make it.