If high-income households squander all the income on eating out, lavish vacations, matching luxury-brand autos, etc., they aren't middle class: their values do not support investing in their children's future, their own retirement (so they won't be a burden to their adult kids) and on building wealth that won't vanish when the current asset bubble bursts.
By my calculation (admittedly coarse, given the huge range of living expenses from lower-cost regions to sky-high locales on the Left and Right Coasts), around $100,000 for state/corporate employed adults (i.e. jobs that provide healthcare and retirement/401K benefits) and $130,000+ for self-employed people (who have to pay their own healthcare and retirement costs) is more or less the minimum required to fund the qualities described above.
It's remarkably easy to earn this income and have very little to show for it by year-end, so this is (at least in many areas) bare-bones.
The Pew report places households with incomes from from $42,000 to $126,000 as middle class. Judging by my estimates, it would very difficult to meet these qualitative standards on $52,000 household income unless housing was nearly free (for example, the family house was owned free and clear and property taxes were low).
In many Left and Right Coast cities, $52,000 is essentially poverty level. Even in lower-cost areas, it would take at least 50% above median household income to fund a middle class life.
Meanwhile, the Federal Reserve's policy of inflating bubbles in assets that were once stable places to build lasting equity (for example, housing) has devastated middle class wealth. Adjusted for inflation (which is likely under-stated, since big-ticket items such as college tuition and healthcare are under-represented in official inflation),