While kidnapping in Iraq is widespread, only a few percent of the victems have been foreigners. Most of the kidnappers are interested in terrorizing families, or entire communities, via kidnapping, or the threat of kidnapping. It is, after all, extortion. Sometimes, money is not involved, but favors, or a change in behavior, is. This is also often the case when foreigners are involved. It's harder to get to foreigners (who are usually guarded, or have friends who can hurt the kidnappers). This is very much the case when diplomats are taken. So far, Sunni Arab terrorists have snatched fifteen diplomatic personnel, usually from Arab countries. The idea here was to convince Arab countries to withdraw their embassies, and thus make Iraq look like an artificial creation of the West. This doesn't work, because nearly all Arab nations know better, and it's hard to ignore several national elections. Grabbing diplomats is something that fringe terrorist groups do, because it causes nothing but trouble for the Sunni Arab community.
The Iraqi Sunni Arab terrorists are supposed to be fighting for the entire Sunni Arab community, in an effort to get Sunni Arabs back in control of Iraq, so that Iraq can continue to protect all Sunni Arabs from Iran (full of non-Arab Iranians, and practitioners of heretical Shia Islam.) When they kidnap an Arab diplomat, the Iraqi government has another reason why no one should lend any support to the Sunni Arab terrorists. The pro-terrorist people in the country of the abducted diplomat are put on the defensive. Grabbing a diplomat tends to be taken as an attack on everyone in the diplomats country.
The largest group of kidnapped foreigners has been contractor personnel. These people are the most exposed. Many were foreigners hired to do work the Iraqis could do, if it were not for the corruption. While hiring Iraqi Sunni Arabs risks getting someone who is a terrorist sympathizer, hiring any Iraqi risks getting someone who will either take a bribe, or can be terrorized (by threats against himself or his family) into betraying you. Most of the contractor personnel are from poor countries, and these guys are making, by their standards, big money, enough to change their lives. Because of the dangers, they are seen of as heroes back home, and when they are kidnapped, it becomes big news back there, and Sunni Arabs take another hit in the opinion polls.
Most of the kidnap victims are recovered, either via ransom, or negotiation. About ten percent of them have been killed.