Are you designing a fold into your pages? If you design around viewport height and position:fix things to the bottom of the screen, then there absolutely is a fold and users will be biased to things above the fold. If your content clearly doesn't end at the bottom of a page, users are perfectly capable of and willing to scroll down to find the rest of the content.
This is primarily an issue I've seen with my students' work. They haven't always internalized the issues with folds, and the need to design around them to make sure that there appears to be a continuous flow of content.
Saying something like "There is no fold" is not going to help students recognize the issue.
I highly doubt we'd see the same breakdown for new users vs. return users. IE, return-users know they can scroll, new-users don't have that knowledge.