Economic explanation of a joke

"What do lesbians call a third date ---- Moving Day"

An old, hoary joke built on stereotypes, but it was floating in the back of my head when I wrote my post concerning rethinking marriage's tax advantages yesterday morning due to this passage and some thinking about incentives:

The quasi fixed costs of living increased far slower than household size so we effectively had higher disposable or at least not immediately accounted for cash flow as a co-habitating and now married couple than we would have had as single individuals.

The gender wage gap means that on average women earn 77% of men in 2006, and any change this year is likely to be small in either direction. This gap starts early as I noted earlier this summer, and it occurs even when controlling for education and career field.

So a woman in a given field is likely to be making less than a man and two women couple are likely to make less than a similiar male-female couple, holding everything else equal.

Is this a partial explanation of the joke --- pooling resources and living together is a way of stretching out incomes that may tend to be smaller than similiar heterosexual couples in the same fields with the same basic qualifications?