Panda,
WHile there are vast area's of America that are quite empty.
If you looked at the population density of the northeast corridor and the west coast you would find population densities that are as high as anywhere in Europe....
The character of the USA is High densities seperated by vast distances. (It didn't take me that much different amount of time to commute to manchester UK when I was based there as it did when I was based in SFO...)
There are more large city/suburb combos from the USA on the top 50 listing then there are from the EU.... And they are seperated by greater distances.
Cheers
Wino