In Newton, Massachusetts, where the Cap’n and I adopted most of our practice and traditions for keeping Judaism modern Orthodox-style, we observed that in about half of the families we knew, the lady of the house said the blessing over the challah on Shabbat (“motzi”). Kiddush was nearly always said by the male head of household (though in at least one household I observed, the woman said kiddush for one of the meals), and in a few households, the male head also said motzi.
In our house, I have continued to say motzi on Shabbat. This is not generally the practice among the English-speaking families we know in Israel. In fact, I may only have seen one other household in the three years we’ve been here where a woman says motzi. But to us it makes sense. We both contribute to the running of the household and the creation of the Shabbat meal. The Cap’n makes kiddush since he does nearly all of the shopping (and grape juice is definitely something we buy rather than make at home). I make motzi since I do nearly all of the food planning, prep, serving, and clean-up. (The Cap’n makes the phone call when we invite people for a meal.) While I rarely make my own challah, it’s symbolic to me of the home-made part of the meal, for which I deserve full credit.
I imagine there must be many reasons for the man to make both kiddush and motzi. Men get most of the speaking parts in Judaism (remember the wedding ceremony?), and this is another speaking part. There is a tradition that a person should say 100 brachot a day, and since this is probably more binding on a man than a woman, this gives him an extra bracha to say. In some households, I suppose the man is considered the founder of the feast, even if his responsibility for it began and ended with earning the money toward it. (This doesn’t hold up in many families today, but families today look less like they did 100 or more years ago, when these practices get cemented into tradition.)
That’s how we do it, anyway. If anyone has more accurate information on why men do both in most households, feel free to share it.
Shimshonit 
Not what you asked, but as I understand it, the theory is that while both men and women have equal chovah in motzi, for kiddush balaliah men are chiyyv d’oraita while women are chiyuv d’rabbanan. (There are problems with that, since in actually the part in which the man is chiyuv d’oraita has already been fulfilled when he said his amidah in arvit, but that’s the general idea.)
I’ve been saying motzi a lot more often recently than Nomi has, although she bakes the challah. Not sure why this has happened; it just has.
We’ll probably end up alternating.
I made motzi for years when DH’s arthritis was so painful he couldn’t slice through the bread. When new meds got the swelling and pain under control, I gave motzi back to him.
The wife of another couple bakes the challah each week, and says motzi each time. “She baked the bread, she should bless the bread.” My challas are also home-made, but I don’t mind either way. In fact, I rather like DH to say motzi because it’s traditional and reminds me of my late Dad.
It sounds from what you all shared as though the motzi-sayer is really determined by the family and its own practices and traditions. In a religion where ceremonial duties are so often determined by sex, it’s nice to have a function that can be shared between husband and wife.
When we made aliyah I took over motzi. I have been baking challah for about a year (not every week, but often); I feel more invested in it now. I figured a huge move was a good opportunity to start some new traditions….