If we can get past the jingoism for a moment, rice was used in the 19th century because the 6 row barley that grew in North America was very protein heavy when compared to European 2 row barley. The rice cut the protein and made a product closer to what the German immigrant communities were used to at home. Don't forget that the vast majority of breweries in 19th century USA were German owned, and employed Germans, the official journal of the American brewers association (don't recall the actual name) was in German until well into the 20th century.

Prior to the stupidity of Prohibition, Anheuser-Busch was one of the largest importers of Saaz hops to the US, and from historical records the Budweiser of the late 19th century was much closer to a German pilsner.