Where I was trying to come from in most of my posts as well. I slipped up and reverted back to America as a whole in my last post.
If South Indians ever end up identifying with and assimilating more with popular culture influenced by black people, then I bet they would also be more likely accepted in saying the word than white people. Being heavily into popular American sports alone can begin influencing how future interactions end up being shaped.
Most important facet influencing all of this is slavery in the United States. None of the people you keep mentioning were black American slave owners. White Americans were the main slave owners, so they are the main people who can't say the word now. That's how I've been told. Fair enough. It just is what it is now. Seems pretty straightforward actually.