There are some 日本动漫 like Case Closed/Detective Conan where the American distributor changed the names to English names because they thought that made the 显示 更多 acceptable to US audiences.
There are also 日本动漫 like Cowboy Bebop and Trigun where the characters have non-Japanese names from the start. I suppose that's because the characters aren't from Japan. Bebop takes place not in Japan, but in outer space, and Trigun on a Wild West type planet. This is all my guessing--I'm not a professional "Answerman" (Or Answerwoman) like they have over at 日本动漫 News Network.