a melting pot?

Every morning while going to work, I encounter diverse forms of human life-a perfect manifestation of the 'melting pot' that the US capital has become in course of several years and this gets me thinking to what extent do the people converging here from literally all over the world, really get assimilated in this melting pot?
There're men and women of all possible shapes,sizes,colors;speaking diverse languages,pursuing different religious faiths,hailing from diverse backgrounds,representing myriad cultures-all converging to this city in search of work,of education,of love,of destiny. The contrasts at times can be so stark that one ends up feeling as if it's a huge circus with participants from all possible countries of the world-countries that I didn't even know existed such as Burkina Faso!
But how much do they really get absorbed in the larger whole? And not just for the capital city-this applies to this entire country, the so-called 'land of opportunities' whose visa-stamp seems a must in the passports of urban citizens of all nationalities.
And having stayed here for a while now, I end up getting the feeling that people from similar cultural backgrounds all still living in their own self-formed tiny islands while hanging out with 'others' -it's a process of voluntary clustering that somehow seems inevitable.
In the capital city for instance, there're strictly demarcated neighborhoods where the residents are of two totally different colors and hence social structures and economic landscapes; the transition from one area to the other is so sudden and abrupt that it can make one feel as if one's walking from one world into another! Everything drastically changes-the houses, the gardens, the people standing in the balconies, the cars parked on the roads, the restaurants and grocery stores, the beggars on the streets, the body language of the people walking on the roads, the slang words used...endless differences! How much do these two worlds living side by side interact with each other? I don't know but from the look of it, it seems they interact only when they have to, at work or in schools-and the follow ups during the happy hours at pubs; but when the time comes to go back home, the subtle segregation becomes so not-so-subtle!
Then there is the omnipresent and gloriously famous for the fake gucci & prada bags-'Chinatown', in every major US city-a section where English ceases to be the 1st language! What is it about the people from our partner-in-crime-country that universally makes them cluster in such a prominent manner wherever they go? And I don't have to reiterate the differences in lifestyle and socio-cultural environment and of course cuisines and even road signs(some of the road signs in NY are actually in Chinese!)-as one moves from the 'city' into the 'chinatown'! And coming from India, I cannot of course ignore the grouping that we Indians do too! Look at Silicon Valley or New Jersey or Lexington Square-from sarees and bindis to pan and mother's pickle-nothing is unavailable in these mini-India's, which at times confuse me-where exactly am I?
Is it economically a more viable option for people hailing from similar backgrounds,to cluster all together in one area in this huge melting pot? or is it because, even if we are far away from our respective motherlands and want to get a taste of 'international exposure' during our pursuit of the 'great American dream', we still want to remain close to people we can relate to without having to spend hours and days trying to explain what we really are?
Maybe the presence of these clusters in some way further facilitate the migration of more and more ambitious young people to this land of dreams, by giving them a sense of security that even though they are willfully getting removed from their own land, they will still be close to their own people?
In a country where the citizens are day and night getting categorized into several isolated camps-liberals or conservatives or neo-cons, yankee-fans or the non-yankees, ivy leaguers or the community college goers, New Yorkers or Californians, techies or wall-street-ers, mormons or scientologists and endless such clusters; maybe it's inevitable that the migrants who constitute such a major proportion of the American population, will continue to have their own separate islands-it's like a mini-world in one country! So maybe after all, we all don't really melt together in this huge melting pot....