This. My impression is that a hard-working person can no longer expect income that supports a family. (I must admit that I have not researched what percentage of working men earn sufficiently much for that now vs. in the past, though.)
[edited to eliminate some unclarity, partly due to my confusing something, but preserving the main statement]
But one of the reasons why it used to be possible for one person to support a family but no longer is is that our standards for what “support a family” means have risen (see also).
If you're willing to be frugal (e.g. spend on yourselves as little as Julia Wise and Jeff Kaufman do) it isn't actually that hard to live on one income in the First World.
Dalrock writes an interesting article related to Dr. Helen Smith's book the Marriage Strike. I really have to bump it up on my too rapidly growing reading list. (^_^)