My hunch is that you're not from the east coast. :) That is, almost all K-12 students in the east coast study the indigenous tribes of the region as a part of state history curriculum and the tribes play an active role in the region with casinos bearing tribes names or concepts (i.e. the Western Door restaurant at the Seneca Casino). Eastern tribes can be seen in films like Last of the Mohicans, The New World, and The Patriot.

As to a why the stereotype of "western" indigenous people is better know, Celluloid Indians by Neva Jacquelyn Kilpatrick is an interesting read.