I think the argument here is that some are referring to GDP & GDP (PPP) while others are referring to GDP Per Capita and GDP (PPP) Per Capita.
In pure GDP/GDP PPP the United States is by far the highest, but as soon as you include the /per capita information though, then the United States would rank somewhere in the 6th-15th range. (depending on the valuation technique).
GDP/GDP PPP PER CAPITA is often used as a proxy for Standard of Living (so that means there are 5-14 countries in the world with a higher Standard of Living than the United States (if you accept this measurement as a proxy for Standard of Living.
On the other hand GPD/GDP PPP measures the health of the entire country's economy as a whole.
So - while the United States might have the highest GDP/GDP PPP - once you roughly allocate that economy to the number of people in the country, then there are definitely countries with more earnings per person.