The Middle Ages aren't "everything that feels old-timey to us 21st century people", they have to be defined by their own inner logic and not in opposition to our present time.
The issue here is that Americans are sundered from the Middle Ages and what it wrought in ways that Europeans are not. It has no real existence in the American imagination other than 'the olden days when there were knights and castles'. As far as most Americans are concerned, Chaucer, Hildegard von Bingen and the Catalan Company are no more real than Robin Hood. Whereas I (for instance) am surrounded by the period's extremely visible legacy; by the ruins of castles and abbeys, by still-extant churches and cathedrals, by woods, boundary-ditches, hedges and fields that the people of the time knew as well as I do, and even by the continuing impact of administrative boundaries first idly sketched out during the period. And one way or another, this is true of everyone else in this continent. The period is part of our living past; it almost feels as if one can reach out and touch it, and in a way, of course, one can. The result is a fundamental divergence in perspective, amongst other things. There is a reason why academic Mediaevalism in North America is such a poisonous pit of stupidity.
Yeah, that might be the one thing about Americans I've had the most trouble relating to. I've been keenly aware of being part of a multi-millenary history since third grade (Our Ancestors the Gauls etc. - though of course I never bought that part for obvious reasons), and that has always been a source of wonder for me, even when modern history became my main interest. It's hard for me to put myself in the shoes of someone from a "young" country whose history is four centuries old at most (of course, the lands they occupy had a much older history, but that history was deliberately destroyed, so those few centuries are all that remains).
Now, stopping at 1945 as Nathan points out is an entirely self-imposed problem, and one that's becoming more and more dangerous as time goes on. I can see an argument for not teaching the last few decades, since it's genuinely hard to put much historical analysis on them, but you people are soon going to miss a full century.
I don't want to defend American history education, and I really don't want to defend the College Board, but I think the latter part is a bit overstated - I remember when taking my AP US and Euro tests five years ago that we had essay questions on the rise of the right from Goldwater to Reagan and the fall of communism in Poland, so it has to be covered unless you want to face the wrath of overambitious gunners.