I strongly suspect you're right. I know that before I could 'grep' digital text, when I remembered something I read in a book, I'd have a rough idea of its page-depth and position on page (in addition to general context) which aided in a visual-scan to re-locate.

Perhaps an e-book interface with stronger indicators of progress could cure the discrepancy. (One idea: shift the entire page slightly inside imbalanced margins based on how deep in the book you are.) Or perhaps people who have only ever read e-books wouldn't be as dependent on pending-pages-physicality.

Or maybe future Kindles could actually become flatter as you progress through the story, via some sort of deflation mechanism.