every government on this world is hiding truth - just as no one needs to know everything. And thats good. Power makes corrupt, money too... And actually one of both is valid for many government members. 
While I agree with what you say, Huor, the movie is about international groups that are more powerful than governments. It is impossible to know for sure, but the theories make sense, based on human nature, and they are more than a little bit frightening. The current global recession and contests/wars over oil benefit a few small, elite, groups of people -- and it is not at all difficult to imagine that those people have powerful leverage over the governments of the world.
The movie is targeted toward an American audience, but it has little to do with America. The hypothetical power groups are international, and more likely centered in Europe, rather than in America. The Freemasons and Illuminati are much older than than the USA.
Think of this movie as a semi-funny satire on world politics. There are some partial truths, and there are some wild leaps that defy logic. It is a mix of sensationalism and reality, and is an extension of some of the thoughts presented in The Da Vinci Code and Lara Croft: Tomb Raider.
The main premise is that there are secret societies, made up of some of the world's most powerful and influential people, who "control" (or influence) governments and economies as they see fit. Nobody votes for them, there is no way for an individual to be "heard" by them, and they answer to no authority other than themselves. Some of the alleged groups are:
- The Bilderberg Group
- Freemasons
- The Illuminati
- Knights Templar (and the heads of the Catholic Church)
- Skull and Bones Society
- Trilateral Commission
- Council on Foreign Relations (CFR)
The Bilderbergs and Freemasons originated in Europe. Skull and Bones is thought to have originated at Yale University, but it is clearly influenced by (and, probably, populated by) historical and family connections to a European base. The Trilateral Commission and the CFR were founded by David Rockefeller, grandson of John D. Rockefeller, the founder of Standard Oil and the guy who made drilling for petroleum one of the largest businesses on Earth.
Is it possible that there may be "secret societies" with the power to influence the global economy and major government decisions? Of course.
It is probable? I think, "yes", given what I know about people. Of course, that is just a guess.
Regarding the details, you should know that the guy who made the movie, Michael Moody, is a Mormon who makes movies about UFOs (and other sensationalistic crap). The Mormon Church is an artificial semi-religion that is loosely based on Judeo-Christianity with some absolute nonsense thrown in by the founder, Joseph Smith. The Mormon "Church of Christ of Latter-Day Saints" was founded less than 200 year ago so that they could claim their own state -- Utah. It is more like an overgrown cult than a real religion, but they have a lot of power and money, and that is more important than logic, apparently.
Moody is also somewhat ignorant. Here is an excerpt from Moody's MySpace site:
College is pathetic and never should exist. I learned everything I needed to know by the time I graduated the 8th grade so why waste another 15 years of our lives with this bullshit?
At one point in the movie, Moody spends several minutes making a bizarre argument that compares birth certificates to berths and their role in Maritime Law. Although "birth" and "berth" are pronounced the same, they are entirely different words, with different roots.
And UFOs... well, there may very well be a few flying around, but most of the discussion about them is fake.
If you don't believe me, then ask Awesomeman what is REALLY going on at the US Air Force Stargate facility in Cheyenne Mountain. But don't be surprised if he refuses to admit to anything. If he knows, it is probably Classified, and he cannot talk about it. 
(just kidding, Awesomeman!)

Here is some more background on the Mormon Church. The funniest part is that it is all 100% accurate. The SouthPark people did not have to exaggerate in order to make fun of the Mormons:
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http://www.youtube.com/watch?v=sHdeR5QKvWU