Absolutely equal. I'm not on vacation - I have a job too. We decided together that I would stay home with our son but honestly I'm married to the kind of guy who would have been happy to be an at-home dad. His career just pays better than mine did!
We do different jobs for our family but we are a team. If anything, I might have more influence over decisions involving money because I am the one who takes care of our finances too - I just tend know more what is going on in that arena.
I think there's a big difference between a SAHM and a "kept woman." I take care of the kid, the house including cleaning, yard work, negotiating with contractors, the money, the insurance, the car, the doctors' appointments, and researching anything needed to make those big decisions. I don't know about your coworker's relationship, but in my marriage, we work equally hard so there's no question about sharing everything else equally.
I would not have married somebody in the first place who didn't treat me as an equal. You make yourself very vulnerable when you drop out of the job market to raise kids. My husband's career has really started to grow. If we divorced, I'd have to start all over from scratch to support myself. I could not have taken that risk with someone didn't really trust. Maybe this situation with your coworker says more about their relationship than about what's typical for a SAHM. I think SAHM's come in all different varieties in this day and age.