Since this is a perception index, I think isolation has a lot to do with it. Americans don't travel much, our news generally ignores countries we're not bombing, etc, and so Americans have very little frame of reference for this sort of judgment.
I personally marvel at what an upstanding and civil government we have, but then again my family is from Bangladesh and we left because my dad was sick of having to do things like pay a bribe to get a phone line installed (we went months without phone service in our house because of his intransigence).
I think you're exactly right. We have a strong, visceral reaction to corruption, and we detect it in everything.
Living in New Mexico can be a bit of an absurd illustration that this isn't a universal view because we tend to have scandals involving these ancient political family dynasties. Whenever one of them is caught handing over a bunch of state contracts to their nephew (nepotism in its truest sense) we get a few great sound bites like "What's the big deal? He's just my nephew!"
In other countries this kind of corruption is seen as simply taking care of one's own or the cost of doing business. I'm glad we overreact to it.
I think it's a good thing too. One of the things I love about Americans is that we're culturally very intolerant of corruption and scandel. I just find it amusing sometimes how people don't know how good they have it.
I personally marvel at what an upstanding and civil government we have, but then again my family is from Bangladesh and we left because my dad was sick of having to do things like pay a bribe to get a phone line installed (we went months without phone service in our house because of his intransigence).