When Susan says:

"I am not sure when it happened, but the division of household chores has become the leading indicator of marital happiness in this country. You'd think it would be shared beliefs and common goals, but somehow we have replaced all the important stuff with who cooks and who cleans up...
but I wish couples were negotiating more important matters -- like how much debt is realistic for Junior's college education, or which one of them is going to do the heavy lifting in the area of sex education."

it's unclear if she is reiterating conclusions from the study that household chores are indicators of marital happiness and have usurped shared beliefs and common goals, or if she draws that conclusion on her own.

It seems to me logical that if a happily married couple already had a shared vision and common goals, it would follow that the couple would have their lives organized in a way that was conducive to the happiness/satisfaction of both partners in the course of meeting those visions and goals. Which would include the division of labor at home.

After all, if a couple cannot work out little things like managing distribution of household duties, without one or the other feeling martyred, resentful or harboring contempt, it seems unlikely they could work through highly charged life circumstances or long-term decisions with any degree of satisfaction.