I think some of the posts in this thread are well-intentioned, but superficial, misleading, and amount to false stereotyping. Yes, dry cleaning businesses in this area tend to be run by Koreans. They also run the best Asian food markets, e. g. H Markets, and what does that prove? I don't think the Asians as a whole are essentially more clannish than other ethnic groups, but when they come here they often have to deal with exploitation, discrimination, language and employment barriers, etc. No wonder they stick together and help each other out. Have you ever lived overseas and see how the Anglos stick together?
That said, there are also distinct differences -- this is superficial but a K-J friend told me once that J girls in the business almost always had a sound business plan for at least a year in the future. How much they needed to make, how much to save, discretionary funds, etc. In her view K girls were more likely to take their $$$ and buy Gucci handbags. I don't know if that's true, but that's what she said.
In NYC, J-girls tend to dominate because there are so many Japanese businessmen there.
This whole topic is a can of worms and I suggest we can the racial stereotypes and stick to basics, i. e. to understand what's going on, just "follow the money!"