It depends. Lots of families need two cars -- but some just prefer it. And as with housing (and everything else), families can often make due with something smaller, older, etc. because it's cheaper.

There is this "modern" expectation of a lifestyle, but most of those things aren't _necessary_. There are lots of families which need two incomes to maintain the necessary stuff, but it's not the majority and few of them are reading HN.