Keep in mind that we're such newcomers that we haven't had nearly as much time to develop a culture as many other places. Add to that our "melting pot" mentality of accepting and adopting other cultures' traditions, and "American Culture" is somewhere between non-existant and hard to define.
I know some who would argue that america is a new imperialist regime, trying to impose their world view through dominance (both military and the media). I know that you can't judge a nation on who's in power, but this is the case.
Sometimes I must wonder if many (most...) of my fellow Americans realize that there is a world outside of our borders. Few American's hold passports, those that do are more likely to travel within the hemisphere, and even when the trip overseas is made, it is to typical, touristy destinations. We are a product of our geography as much as we are a product of our own pride. After World War II, the US underwent a two decade boom unprecedented in human history. Our population and wealth grew to a point where we became even more self-sufficient than before, even as we were coming in contact with more of the world. In terms of many manufactured goods, we're different from the rest of the world not because everything we have is better, but because we form a large enough market to support any given product. I think TVs are even now measured in inches all over the world, right? I am not sure anybody makes (good...) TVs in the US any more, but we're a big market and our influence is still felt. Then again, being isolated and self-centered sounds awful, and in terms of a good intellectual education about the world, it is. but it was an outgrowth not of a bad attitude, or a superior attitude, but simple self-sufficiency. Americans often didn't speak a second language, especially in the second half of the twentieth century. French and German people spoke two or three in most cases. Was that because the Americans are jerks and the Europeans are well educated and urbane? Of course not. It's because an American could live an entire lifetime in the US and never come across anybody who didn't speak his language. Of course this extended to cultural issues as well; no need to understand how or when to bow or why to not eat with one's left hand, if you literally never encountered anyone who had different customs than you.
With all of this said, the point I make is this: Americans have a great deal of pride in their country and are unafraid to shout that pride from the rooftops (Hence the popularity of Toby Keith, lol). That pride may be romanticized/exaggerated, even groaned at by other countries, but we carry on with our pride because we wear it on our sleeves.