My point is there's plenty of good content people want that's 30-70 years old & they don't feel bad about pirating it. My dad by his principles would never download a new movie; nevertheless he's looking up the songs from his childhood on YouTube. He feels entitled to listen to them whenever and however he wants. I think that's a pretty common attitude toward the older stuff.
You're probably right for everything produced since the second World War, but I doubt people think that e.g. Triumph of the Will is under copyright. I think people have a vague notion of "historical" vs. "contemporary" that starts right around the end of WWII.