Which really only perpetuates the stereotype that Americans are an insular bunch and only look at things with America is the best ev-ah tunnel vision.
And just like every other stereotype, it takes much less to "prove" it than it does to disprove it. Even if 70% of a group one is being stereotypical about holds a certain trait, especially a negative trait, we're doing the remaining 30% a disservice by assuming that they hold that trait. But it's human nature to categorize things. It's part of how we have been able to streamline judgement to allow time to think about other things as well as being able to make decisions without having innate instinctual knowledge without having to stop and waste valuable survival time making judgements about danger, which route to take, etc. It doesn't always translate into moving beyond idiotic tribalism though (whether it's on Americans' part or otherwise).
As far as WWII is concerned, it's been interesting to get another perspective on it, and I am not necessarily thinking of just the British view. I think I already knew about the resentment about America's isolationism and profiteering created in Europe, and how many Americans downplay the role of the UK and the USSR in Germany's defeat (not to mention having multiple fronts). What I didn't really know was the ongoing bitterness about war reparations and just how unprepared the US was when it first entered.
As for insularity, I think it is more complicated than people outside the US actually understand it to be. For instance, some things don't translate well. A foreign holiday for many Americans isn't always a matter of driving a few hundred miles, taking a train, or a short hop on an air plane. In fact, the oft quoted statistic about Americans and passports ignores the fact that most of North America and the Caribbean was accessible to Americans with their driver's licence and birth certificate (and sometimes just their driver's licence). It wasn't until the past decade as requirements have been changed that Americans have been forced to get passports to go to Canada, Mexico, or many of the islands.
Karrit (giving credit where it's due

) always makes the good point that holidays in the US are for most people two weeks a year, most of the time not taken together. When you consider the distances travelled just to get out of the US, that adds up to at least a day of travel out of that short holiday just to get on their way for people in some areas of the US. Even visiting the east coast means that I spend about 20 hours travel time each way (adding travel to Heathrow, getting to the airport early for checks, the travel, layover--or in my case travel to train--final leg and then reverse on the way home to the UK).
I don't want to go on and on about this, but earlier this year Nigel Farage (of UKIP and air crash fame) went on BBC QT and mentioned how insular Americans were. They have papers that only cover local news and nothing outside a 50 mile radius! Far be it from me to call Mr Farage a bigoted idiot who was trying to directly translate something that had a different cultural role in the US, but of course local papers cover local news. It's a bit like ignoring
The Times or
The Independent and using "The Turnbridge Wells Gazette" as an example of all printed media in the UK. The regional and national papers cover the national and international news (not to mention the much larger broadcast media).

But it is much easier for people to think that Farrage speaks the truth because it "proves" what people already know about Americans: they are insular idiots who care nothing about something that occurs a few miles from their dooryard.
TL;DR-People are people. We're shaped a bit by culture and circumstance, but nothing is ever a universal trait in a culture unless it's a human trait (like prejudice).