My husband is Sicilian American. 3rd gen. There were genuine Mafia from NYC at his grandfather's funeral. His grandfather moved to the country in upstate NY to get outside the family and be an honest American. And that's what this branch of the family is. Honest Italian/Sicilian Americans.
There are however significant differences in Italian American cuisine and Italian or Sicilian cuisine no matter how you slice it... and that's not me saying Italian American's are "dolt's who eat at Olive Garden" in any way. Just that there are major differences.
Italian American food is more reliant on pasta and bread products, and less reliant on variety and fresh foods. There is not the wide variety of regional differences either. Where as you can go into just about any generic "Italian" restaurant in America and order the same things off the menu unless it's a really specialty place that does genuine regional Italian foods, you do not get that in Italy... menus will be different there reflecting the local culture.
My husband, Sicilian American himself and having spent a good amount of time in Italy has expressed this same sentiment... and we have discussed it with his mother during dinners with her and she agrees... Being 100% second generation Sicilian American I think her opinion is pretty valid.
Saying there are differences is not insulting. It's just saying there are differences.
You wouldn't say that American hot dogs are exactly the same thing as the German Weiners they were based on would you? I certainly hope not...