I will agree that for the most part LA has SF beat on Asian food, but Cantonese/HK style Chinese is better in SF, and the rest is probably on par, just fewer options in SF.
But you nailed in on the head -- you have to find ethnic food made by people who know how it's supposed to taste and making it for people who know how it's supposed to taste. If I go into an ethnic restaurant I know it's good if the majority of the customers are that ethnicity.
Seattle seems to be more authentically Japanese than other places. I found a ramen booth place in Capital Hill like Ichiran where everyone eats inside a curtain.
SF Japantown feels old and rundown like nobody's moving there anymore.
