Growing up in New York we had 'mexican food' places, but when i moved to the Southwest and So Cal I learned that they were American Mexican places back on the east coast. I really decided I loved Mexican food when I moved to states on the actual Mexican border.
Then I started traveling in Mexico and learned that even border towns in the US can't quite capture the freshness of Mexican Food in Mexico.
I suppose it's like anything else. The closer you get in distance to something the more authentic it gets. Guinness beer in the UK, for example, is FAR superior to the Guinness they export.