I agree with your statement about two household incomes vs. one, but the standard of living in the U.S. is exponentially higher today than it was in 1970.
(US per capita gdp in 2003 dollars)
1960 - $14,960
1965 - $17,748
1970 - $19,879
1975 - $21,575
1980 - $24,500
1985 - $27,435
1990 - $30,729
1995 - $32,564
2000 - $37,572
If you look at household incomes, adjusted for inflation since 1970, you'll see its marginal increased at best.. and if you take into account that now most homes are 2 income vs 1 income back then you see that earnings is declining per person. when it takes 2 folks to just break even with what 1 person was managing to do 35 years ago... you aren't gaining ground.