American intelligence agencies have long known of this custom. During the Cold War, security clearances for foreign born Americans were often held up, or denied, because the applicant had close kin back in the old country. The American "take the nuclear scientist out of the country" ploy was apparently intended as a PR gimmick. In the real world of intelligence gathering, questioning one of Saddam's weapons experts anywhere, without guaranteeing the safety of his extended family, would probably not work. At least it wouldn't work as intended. There are other ways to make the guy talk. For example, you tell him that unless he comes clean, you will leak info to the Iraqis that he did talk. If you have some good information about what a weapons expert knows, you can use that to test if he is telling the truth, and make good on your threat to "taint" him and arouse the painful suspicions of the Iraqi secret police. It's a dirty business, extracting information this way, but if you want the data bad enough, that's how it's done.
The UN resolution that renewed the weapons inspections of Iraq included, at American insistence, the authority to take Iraqi scientists and technicians out of the country for questioning. This procedure allows the UN to take the subjects family out with him. What this overlooked was that the concept of family is different in Iraq, as it is in many parts of the world. An Iraqis family includes not just wife and kids, but also parents, aunts and uncles and cousins. Any of these are subject to abuse by the government if some other member of the family does something the government does not like. This custom of group (family) punishment is an ancient one and is still practiced in Iraq. In fact, it's a key element in controlling the Iraqi population. Mess with Saddam and you can expect your family (and yourself, if they catch you) to suffer for it.