I agree -- I don't understand why they thought American kids would be too dumb to figure out what British slang meant but Canadian kids weren't. The school systems here aren't THAT bad.
I read tons of books with British words and slang in them when I was little and I figured out what "loo" and "jumper" and "anorak" were by the context. I don't think kids have gotten that much stupider since I was one, either.
I think it just goes along with the American culture of dumbing things down to the lowest common denominator. People think that everything should be as easy and enjoyable as possible -- there are so many people who don't realize that if you put a little bit of effort into something it often makes it that much more enjoyable, and it challenges you to do something that you haven't done before or learn something that you haven't learned before. Unfortunately, this part of our culture -- the part that says that learning doesn't have to be a chore, or that hard work isn't always something to avoid -- is quickly becoming nonexistent. But that could lead me into an entirely new rant, I think.