While it's true that the average population density of the US is low compared to much of the rest of the world, that is due to including the US's vast empty spaces, mainly in the West. The vast majority of US citizens live in densely populated areas - just like the rest of the First World, only with crappier internet.
The population density is still radically different even when you cut the vast empty spaces between cities in the west.
I live in a midwestern suburb. In the land area that my house uses, you'd have 10-20 families in Madrid. Our idea of dense shopping is a two story mall, not stores under every residential area. And don't get me started with mandated parking spots in strip malls that aren't ever half full.
So unless you live in Manhattan or downtown Chicago, you don't see the same levels of population density.
Population density is still a red-herring in this discussion though. Internet connections in Manhattan are worse than those in small cities in Romania, yet Manhattan is 3-12 times more dense than Timișoara and Bucharest.
