Ridiculous. I admit that the fact of her gender likely only matters to dinosaurs raised in another age...and one's upbringing is not an easy thing to overcome...but are you seriously suggesting that if another person, regardless of gender and regardless of motivation, strikes you that you are going to respond in the same manner each time? I'll say it again: ridiculous.
The response will be modified to suit the circumstances. You aren't going to react to a 15-year-old kid or an 80-year-old drunk the same way you would to a healthy adult man your own size. You need to use judgment...and when this jerk took a slap from his wife...paused a split second...and then whacked her once, and swung and half-missed again, and then appeared to be trying to follow through yet again...he proved that his judgment is not to be trusted.
She absolutely should have been able to make a better choice. So should he...and it's more important in his case because he can do more damage.
Your entire argument sounds like "Well...she started it!"