One interesting observation that supports this is that women's labor rate participation had a slower ramp. Not a doubling over night. Following that, their wage equality has slowly been ramping, too. Both of those sound like gradual dilutive trends on the labor supply/wage graph.
I REALLY like the idea of looking the cumulative burden of employer-born costs of employees as the percentage of dual earners goes up.
my "bet" is that you'd find that the cost of those benefits have been growing at par with the women's labor force participation rate. Take a look at the charts in the Slate Star Codex post on Cost Disease, and overlay the growth in Women's labor force participation rate, and growing pay equality. The relationship is likely not perfectly causal, but there might be a meaningful effect in there.