http://www.nytimes.com/2012/06/13/world/europe/13iht-letter13.html?_r=3&smid=pl-share
"Today, across the member countries of the O.E.C.D., 40 percent of couples in which both partners work belong to the same or a neighboring earnings bracket, compared with 33 percent two decades ago, a 2011 report by the agency shows. Nearly two-thirds of couples have the same level of educational attainment (in 15 percent of the cases, the wife is more educated than her husband).
Doctors used to marry nurses. Now doctors marry doctors.
So while husbands and wives have become more equal, inequality between families appears to be on the rise. As Christine R. Schwartz, a professor of sociology at the University of Wisconsin, puts it: “Marriages are increasingly likely to consist of two high- or two low-earning partners,” rather than of one of each."