When I mentioned assimilation, I meant a certain acceptance of the American culture. I did not in any way mean complete abandonment of your "native" culture.
One of the most obvious things I saw different about Americans is their sense of individuality; you'd see a super conservative person living next to a hippie in peaceful co-existence (although these days the media would make you think otherwise).
As an example, I'm mostly vegetarian (for staying healthy, I'm atheist) but I do like the occasional steak. If I say to a fellow Indian (or naturalized Indian American) that I eat beef, I will be mostly ostracized (I'm assuming that this person is Hindu, which may not be the case). I personally don't care what anyone thinks about my personal choices, but this is an example of people not assimilating and accepting what is generally accepted American trait of "individuality".