Well, this "richest country in the world" business is somewhat misleading. It means the country with the greatest aggregate economic power, not the country where people tend to be the best off. You need to look at several measures before you can begin to understand the thing that's mystifying you.
By total GDP the US is by far the wealthiest nation in the world. It has almost twice the total GDP of the second country on the list, China. By *per capita* GDP, the US is about 10th on the list, just below Switzerland; so by global standards the typical American is wealthy, but not the wealthiest. On the other hand the US ranks about 20th in cost of living, so the typical American has it pretty good.
Where things get interesting is if you look at GINI -- a measure of economic disparity. The most equal countries are of course the Scandinavians, with Denmark, Sweden and Norway topping the list. The US is far from the *least* equal (Seychelles, South Africa, and Comoros), but it is kind of surprising when you look at countries near the US on the list. Normally in most economic measures you see the US ranked near advanced industrialized countries in Europe, but it's neighbors on the GINI list are places like Turkmenistan, Qatar, and El Salvador.
What this means is that we have significant classes on either end of the scale: the *very* wealthy and an economic underclass. Now because of the total wealth sloshing around in the US, the US underclass has it pretty well compared to the underclass in, say, India. But what this doesn't buy is clout or respect. "Poor" households in the US usually have TVs and refrigerators -- a fact that seems to anger some people, who see the poor in the US as ungrateful people who are too lazy to improve themselves. But a study by the OECD suggests that they don't have the *time* to improve themselves. In a ranking of countries by time spend on leisure and self-care the US ranks 33rd, at 14.3 hours lagging almost two hours per day behind world leader Denmark (big surprise). But remember this is an average; it doesn't represent the time available for the poor.
Most Americans seem to think that poor people spend all their time sitting around waiting for handouts. This willfully ignores the phenomenon of the working poor. After selling my company, I volunteered on a lark at a charity which refurbishes old furniture and household stuff and furnishes the homes of poor people, and I found poor people to be neither lazy nor ungrateful. Let me tell you I have never met so many people who work two or sometimes more jobs. Particularly shocking were the number of women who took their children out of abusive relationships, and then have to work a full time job, raise three or four kids, without a car and in a neighborhood that doesn't have a grocery store. You don't know what gratitude is until you've given a poor, overtaxed mother beds when her children have been sleeping on the floor for months.
When some smug, ignorant and conspicuously well-fed media head starts whining about the poor having refrigerators, it makes me want to punch them in the mouth.