The affluence of ordinary Americans has long been one of the most powerful advertisements for the American way of life. When Richard Nixon debated with Nikita Khrushchev in Moscow in 1959, he conceded that the Soviet Union might have outstripped the US “in the development of the thrust of your rockets for the investigation of outer space”, but he proudly pointed to colour televisions and kitchen appliances as examples of his own country’s prowess.

When I was an exchange student in the former Soviet Union 30 years later, America’s private prosperity remained an important part of its appeal. In the Kiev of that era, it was still dangerous to associate with foreigners, so my friends were mostly dissidents and their supporters. Yet even in this highly politicised milieu, the material comforts of my life back home were among their chief preoccupations.

That experience may be one reason I have always had a soft spot for America’s consumer culture. I am a reluctant shopper (probably because of my dubious and uncertain aesthetic judgment), but, as a matter of principle, I love this country’s commercial cornucopia. Freedom of choice in the check-out aisle is not so very far from freedom of choice in the bookstore or cyberspace or the voting booth. And I agree with Nixon’s assertion that one of the glories of American consumerism is the idea that luxuries – colour TVs then, iPods now – should be within reach of most of the population.

So it is with some sadness that I note that America’s age of indulgence seems to be giving way to an era of frugality. Earlier this month, for instance, Lee Scott, chief executive of Wal-Mart, told me and my colleagues that his careful customers had started to switch from buying 32oz pasta packages to the 48oz size, with a lower price per ounce. Martha Stewart’s fans appear to be feeling the squeeze, too. According to Susan Lyne, the chief executive of Stewart’s eponymous company, they have started to ask for recipes that use less lavish ingredients. This is still the US, so some of the country’s penny-pinchers have even adopted religious language to describe their personal finance conversions. Natalie McNeal, a Miami Herald reporter, says she has taken a “vow of frugality” and is sharing her struggle to spend less with readers of her blog, “the Frugalista Files” (one of this week’s dilemmas was whether forking out $16 on a shirt was OK).

America’s economy is slowing down and probably going into recession, so it is hardly astonishing that its once tireless consumers are calling a time-out. But the shift Americans need to make – and may be making – is bigger than adjusting to a temporary period of smaller paychecks and greater economic insecurity. The financial crisis has many complex explanations, but it also has a very simple one. As former Fed boss Paul Volcker put it in a rare speech last week, “It is the United States as a whole that has become addicted to spending and consuming beyond its capacity to produce.” This equation doesn’t take a PhD in economics to appreciate. McNeal’s blog is more concerned with scoring free pastries at Dunkin’ Donuts than resolving global financial imbalances but she, too, has reached the Volcker conclusion: “Too many of us are spending too easily, without any thoughts about our financial future ... The result? The nasty gift that keeps on giving: a credit card balance.”

American Frugalistas will certainly be personally better off if they can stick to their vows, and, in the medium term, so will the economies of America and the world. But this necessary readjustment won’t be pain-free. For one thing, pretty much everyone is hoping that US consumers don’t take the cold-turkey approach to their spending addictions – hence the $600 tax rebate the government is sending them in June; a fiscal stimulus designed to be spent, not saved.

Perhaps more importantly, the easy credit so many American households have enjoyed may have masked one of the most troubling aspects of the country’s go-go capitalism. That is the fact that, even as the economy overall has expanded, and the rewards reaped by America’s most talented – or luckiest – citizens have ballooned, median household income seems to have stagnated.

In his debate with Khrushchev, Nixon knew it was important to insist that his country’s consumer delights were affordable to “any steelworker”. A strength of American capitalism has long been its cultural instinct to hold up its super-successful as heroes, not villains. That attitude rested on powerful assumptions about equality of opportunity, and the idea that even if they weren’t plutocrats, ordinary, hard-working folks would do alright. McNeal seems to be surviving without another pair of the peep-toe pumps she adores, but if people like her start to feel the economic deck is fundamentally stacked against them, the political consequences will go a long way beyond fashion.

One of the pleasures of writing this column has been the chance to communicate directly with so many readers. This is my last A-Train, but I hope you will continue to send your ideas to me at: chrystia.freeland@ft.com