I don't think people need to have cultural similarity for a well-functioning business. I think the diversity really helps businesses be successful for several reasons:
1) Diverse people come at problems from different directions. That's not just cultural diversity, but all kinds of diversity. The best-run businesses have cross-disciplinary, cross-cultural, cross-cutting teams.
2) Diverse teams understand markets better. Most Silicon Valley startups are focused on the same demographics: Wealthy, liberal Americans. A lot of other groups, both within the US and outside, form huge markets which are underserved, and business opportunities.
I've been in cross-cultural organizations, and it can work really well.
And yes, just as with your experience, I do find a lot less cultural adaptation working with immigrants (not just "Indian engineers") than with locals from cultures other than my own (not just "religious white people in the United States"). Immigrants are in a different culture, and already making cultural adaptations. They overlook a lot of irrelevant stuff, and when they do react, it's for things less subtle.
Working across cultures when people look like you, and expect you to behave like them is a lot harder. And in many cases, the differences are subtle but important; a word takes on a slightly different meaning, or body languages is slightly different. That's actually a lot harder than when both people know it's a different culture.
The comments about cancelling weren't about you. Someone else went in and all my posts were marked with a huge number of downvotes. That's either someone with multiple accounts or a bot. Not sure which. They seem to be back to normal now, so perhaps other people upvoted, or perhaps a mod fixed it.
Regarding other countries, I think it's a bit sad when local cultures get stamped out or Westernized. I don't mind Japan being for Japanese, or Ethiopia Ethiopian. I appreciate that kind of diversity too (not everywhere needs to be tolerant). The US is different because it's a nation of immigrants, and the culture should be a melting pot. I want the US, where I live, to be tolerant. I don't apply that standard to others.