3 anecdotes sum up my thoughts on this:
I once had a Japanese social anthropology class that prompted us to go to a Japanese restaurant and write an essay on how authentic the experience was. Having recently been to Japan, I felt particularly well prepared for this assignment, and proceeded to point out all of the things about the American restaurant that failed to meet my standard for an "authentic" Japanese experience, from the fact that it was owned by Koreans and staffed with Mexicans to the variety of dishes on the menu and the ingredients that you'd never see in Japan. I got the paper back with a surprising amount of red marks, and the next class was all about how the illusion of authenticity and comparison blinds us to the actual authentic experience that we ARE having. No Japanese restaurant in America is authentically Japanese, no matter how well trained their chefs, or have their fish flown in fresh daily, or whether they imported ticket machines and decor from Japan. You're in America, give up on having an authentic Japanese experience here. You're paying (and tipping) in dollars, and driving to your reservation on the right side of the road. Just enjoy it for what it is.
And this brings me to the next point. I have a Japanese friend who came here to study in college and later married an American. We went to dinner once and he suggested an all-you-can-eat sushi buffet. I was surprised that he wanted to go to a restaurant that butchered his country's dish with low quality ingredients hidden behind sauces and overwhelming flavors, and what he told me has stuck with me ever since.
"American sushi... is not sushi. It's junk food, and it's great junk food. That's what America excels at." This point drove home what my teacher had been trying to show us all those years ago. We went and had a great time.
That point is that every restaurant everywhere has a duty to its patrons, to appeal to their palates, and to serve them options so that everyone can order something they want. In Japan, if you want tempura you don't go to a ramen shop or a sushi restaurant. In America, restaurants don't specialize, they try to serve something for everyone, because people bring their families and their picky friends to eat together. In Japan, you don't ask for substitutions and make special requests, you go to that restaurant BECAUSE they have been making that dish in the pursuit of perfecting their recipe. In America, the customer gets what they want. In a sense, you'll never have that "authentic Japanese" restaurant experience elsewhere, because the very nature of the service is fundamentally different, and you are not a Japanese patron who grew up with these norms. It's not a qualitative argument, it's just different.
Lastly, on another trip I was visiting a friend in Santiago, Chile, and they said "let's get sushi, I love sushi!" As we perused the menu, I noticed that EVERY. SINGLE. ROLL on their menu had cream cheese in it. Count your blessings.
Cuisine isn't something static, dogmatic, or monolithic but creative and vibrant, as evidenced by Japan's dynamic urban gastronomy. Japanese fusion brought us omurice, Chinese ramen and gyoza, Japanese curry, yakisoba, teriyaki burgers and teriyaki pizza, and Spaghetti Napolitan.
