Exponentially? I do not think that word means what you think it means.
First, we have to define whom we are discussing, when we talk about the poor in the US. Homeless people, for example, are just as bad off as they have ever been.
If we go up a notch, then we're basically dealing with people who are literally 1 or 2 paychecks away from homelessness. These individuals have cell phones, sure, because you basically can't get a job these days without one. They get cheap phones with prepaid plans. They don't have SUVs and big screen TVs and closets full of clothes. They work for a living, whenever possible, in part because getting anything more than food stamps is difficult, time-consuming, resource-consuming, and results in little benefit.
This is not a group whose standard of living has grown over the years. In fact, they do worse, because it's much more difficult to get government assistance when they need it. Most of these individuals are unskilled, which means their wages have been flat for decades, and lower than what unskilled (e.g. factory) work in the 1960s and earlier.
I suggest you read
$2.00 a Day: Living on Almost Nothing in America to get a glimpse of that kind of life.
Let's go up another notch. Now we're looking at people who can afford a home (probably rented), can afford food, are employed (or on a fixed income), have access to a car or public transportation, and can go for maybe 2-4 months of unemployment before running into serious trouble. As noted above, much of what is used to tag them as affluent is dirt cheap these days. TVs, radios, cell phones are all cheap one-time costs. (A brand-new 30" Samsung TV at Walmart costs $160, by the way.)
Has their quality of living expanded
exponentially? I don't see it. As above, unskilled work pays less, and employment overall is less secure. Education is increasingly necessary and expensive. Lower-income families have had televisions and landlines and cars for decades now. Cheap entertainment has been around for decades; a movie ticket in the 30s cost $0.35 or so, which is equivalent to $6 today. Other costs, such as medicine, child care, elderly care, and education have shot through the roof.
All these changes are happening while women have increasingly entered the workforce. In the 50s and 60s, one income was sufficient to keep a family's finances stable; today, that often requires
two incomes.
There are other complex shifts here as well. In the past, credit was rarely used, and families tended to save money. Today, that two-earner medium-income family can only stay afloat because they have access to credit. Today,
60% of Americans don't even have $1000 on hand for emergencies.
So, I'm pretty confident that most of the poor are not doing substantially better today than in recent decades. It seems like the "exponential" leap was around 1945-1960, when there was an explosion in the availability of consumer goods, as well as some more gradual changes from roughly 1870 - 1920 due to increased industrialization and regulation in the US.
