Bravo to Megan McArdle for this: When Bread Bags Weren't Funny:
The Ingalls family were in many ways bourgeoisie: educated by the standards of the day, active in community leadership, landowners. And they had nothing.
There's a scene in one of the books where Laura is excited to get her own tin cup for Christmas, because she previously had to share with her sister. Think about that. No, go into your kitchen and look at your dishes. Then imagine if you had three kids, four plates and three cups, because buying another cup was simply beyond your household budget -- because a single cup for your kid to drink out of represented not a few hours of work, but a substantial fraction of your annual earnings, the kind of money you really had to think hard before spending.