I think you are right.. one example of culture is in most of the world profit is looked at as a bad thing.. or outright evil. So they can't rationally allocate capital with the profit incentive. Or build up capital for that matter.
Merit is another huge factor. I've noticed in America the average person isn't too bright.. but we do have many ultra-bright people and we manage to get them in positions of power, or back them with venture funding. In most of the world your place in society is determined by who your father was.
Still even if we argue it is completely cultural based.. the new arrivals may carry with them their old culture. For example the Mexicans waving their mexican flags and holding up Che Guevera posters.
Its not that I'm against immigration, we should have many coming, but I think it wouldn't hurt to ask which groups are being a net benefit and why.. and weight towards them.