True the term is all inclusive.   However, there is a different meaning that is frequently interpreted when people state, "we're all the same," or "we're all just Americans now."    What people hear is, "No one should ever have ANYTHING that isn't available to ALL Americans."   

There are very good reasons that Native people have some separate laws and rights, and they are moral reasons and based in justice, however mean some of them might be.   Even the authors of the Constitution established a separate relationship between the US and Indian tribes in the Constitution.   On paper, at least, they are still sovereign nations with rights of their own.   Changing that won't make us "all just Americans," either, an unfortunate perspective that promotes ongoing resentment and bigotry.    It's how we keep it alive.

Language confuses us greatly.