As the U.S. population crossed the 300 million mark sometime around 7:46 a.m. Tuesday (according to the U.S. Census Bureau), the typical family is doing a whole lot better than families were in 1967, the year the population surpassed 200 million. Mr. and Mrs. Median's $46,326 in annual income is 32% higher than their mid-1960s counterparts, when adjusted for inflation, and 13% more than those at the median in the economic boom year of 1985. And thanks to ballooning real-estate values, average household net worth has increased even faster. The typical American household has a net worth of $465,970, up...