bigger country, possibly more people, and more people may lead to more money than what is possible to Japan...wait never mind forgot that ppl don't pay for Naruto in the US...silly me.
Not fair to compare, Look at the Japanese population and the American population basically a 5 to 1 ratio or more their more Americans than Japanese. For a true scientific comparison you need 2 counties with close to equal population to compare as for the number of Manga readers.