Yes I get what you mean. To raise children well, to have time and energy to shape their characters, is part of being able to 'afford' them. Lots of people seem to think it's just affording to feed and clothe them. No matter what your financial situation, a 3rd will stretch your resources. Often people don't plan ahead either, eg have savings and insurance, in case a parent is ill and can't work for months, or a nanny is needed. It's not unusual to go from affluent to poverty these days.
For parents who employ a full time nanny, I think that solves the issue as a good nanny will focus on personal care, appointments, character, manners, laundry, bedding, new clothes, nutrition etc. Because her job is soley about raising the children, she doesn't have to worry about the rest of the household like a SAHM does