I don't think it is very difficult for people from IITs, because they follow basically the same pattern as colleges in US. But, other people may find it difficult because they are not used to so many assignments, quizzes, and exams at regular intervals. Once you become used to it, it is much easier to score in US universities because of "continuous" evaluation rather than Indian universities which have exams once a semester/year.
I like to blog about various topics ranging from education in IITs to social issues in India and US. All opinions and views presented here are my own and not of my employer.