I think it’s less likely to be intentional historical revisionism, and more likely that Hanlon’s razor applies:
If schools deviate they risk losing funding...and frankly most teachers are happy to read from a script.
In fact, I would invite you to take a look at the common core standards for English/Language Arts. They are hardly a curriculum script. They offer significant flexibility and opportunity to individualize content for your teaching context. Despite all the problems and issues I face on an average day, being pressured to teach canned curriculum is not one of them.
The other unfortunate side of AP classes is that much of history classes is taught well before the AP class. I had 2.5 years of history in high school: One semester was a law education class, only offered to "advanced" students instead of geography (a real shame, as I think the class was one of the more helpful classes I took), one European history class, and one AP American History.
The American History class was the most interesting and probably the most free, actually. My particular class used a college-level book and the teacher would add in things that weren't covered by the book and she'd point out where the book might be misleading or wrong. That class was also where I was introduced to "The Jungle", "Grapes of wrath", and Malcolm X's biography.
I oddly don't remember as much about the actual test (it was 20 years ago), but it wasn't nearly the same as other standardized tests at the time. If I remember correctly, it was more based on thinking and processing history than memorizing facts.
Here's a listing of the tests given in VA... http://www.doe.virginia.gov/testing/sol/released_tests/index...
A significant portion of my family is made of teachers and this is not true at all. In healthy (most) schools, teachers have enough wiggle room to tell students "This portion of your textbook is wrong/biased in a weird way". In some cases, they may be prohibited from saying specific things and other oddities, often by old and angry boards of education or similar, but if an educator actually believes in the importance of teaching children, they will find a way to impart the needed knowledge.
You can easily see this in situations like how heavily underpaid teachers still go out and purchase their own supplies because the schools do not give them the tools to do their jobs. Many teachers go above and beyond what their contract states.
Remember that teachers have often seen multiple different education standards and decrees come and go, and therefore understand actually educating is more important than meeting the minimum standard