I don't think it's because people are idiots, I think it's more to do with two things:
1. Not enough people vote. Then you end up with a government that doesn't represent most people.
2. Not enough political parties. Then you end up with poor choices, which makes people not want to vote. This stems from the fact that one must raise zillions of dollars to run for office, which means that a major portion of the populace do not have a voice. Most Americans just do not have zillions of dollars, and those people can not only not run for office, but they feel alienated from those that do have the money to run.
Some of my best friends in this world are Americans. Some of them are not so swift, but most of them are just as intelligent as any of us. Some even smarter. The difference between them and some of my non-US friends is that even those American friends who are smart, are not educated (can't afford it), and many of those who are, feel so alienated that they do not vote. Apathy is the prevailing feeling I get from discussing politics with them. Voter reform is easier said than done in countries where the currency rules who gets into office, though, so it's a bit of a catch 22. That's just my opinion.
I remember coming to Canada in my late teens and being totally shocked at how little political involvement my peers had. Shit, when I was in high school, we had mock elections, and the political parties sent out representatives to debate in the cafeteria. We were all very involved. By the time we got to college, we were politically active in the youth branches of the various political parties. We also had a 98% voter turnout back then. I don't know what it's like now. I just know that we thought that our votes counted and that it was important to vote. I think that has to do with the old Norse system of the Thing, and everyone having a voice at the Thing, which made us Scandinavians different from other peoples of that era. It was not a duty, but an honour, and it was also a rite of passage to finally get to vote. It was empowering as hell. I don't see anything like that either in Canada or the US, wich is very unfortunate. Your people have fought hard as hell for your right to vote, and not just Rosa Parks and other black people, but I believe the war of independence was fought for the principle of no taxation without representation. It's just fucking sad that nobody ever remembers that it is not a duty, it is an honour to vote, and that you've got such pissy choices to choose from. Franklin and Washington would be turning over in their graves if they knew...