Hah, I wish that were true. Supermarkets exist to make money, so they can't stock items that have low demand. If you cook ethnic foods, you'll typically need to visit several stores to buy all the ingredients for your meal.
Judging from flog's reply to my comment it's a cultural thing. In the UK the main supermarkets all have sections for ethnic foods (as the number of polish immigrants has increased for example the supermarkets have added polish food sections). Things in the US market seem to work differently.
