That’s only sort of true, now, and less so each year. The issue is the latter group you mentioned: readers. Even if certain genres, tropes, idioms and idiosyncrasies were unique to the culture, the novels themselves share that culture with the rest of the world, and readers who experience it go on to write their own stories heavily influenced by what they’ve read. We’ve started to see originals crop up from western authors that look remarkably similar to those of eastern origin. As time passes, it matters less and less where you were born, and more and more simply what you’ve been exposed to.