Earlier quoted context omitted.
Both can be true at once. The richest are farther ahead than the richest were, in monetary terms, but the poor have made huge strides in absolute wealth as well: it's possible to live a 1950s upper middle class lifestyle on almost the same dollar amount in 2013. Our idea of what a middle-class lifestyle entails, though, is now far above that.
Well, there are also intangibles that nobody cares to measure, that matter a lot. A 2013 "middle class lifestyle" might be far ahead a 1950 "middle class lifestyle" in pocessions, access to products, etc, but there are important differences too. For example, in all likely the 1950 "middle class" family could get all they needed by only one person working. And that person work an 8 hour day, with benefits and security…
Keep in mind that this is only a couple of decades (at most) from the Great Depression. Even if the 1950s were clearly better, it's a rather cherry-picked data point considering how much worse the 1930s clearly were.
That being said, I'm not too excited about the intangibles of the 1950s. The Korean War was in the 1950s and Jim Crow was in full swing. Life expectancy was much lower. Just about any consumer good from today is clearly superior to the 1950s equivalent.