I wouldn't call that completely accurate. Some people may get up for other reasons, like the intensity is too much and they need a break. Also long movies are unkind to people with various physical issues, not all tied to elimination. But if you're seeing the number drop as you edit the movie, that probably does mean it's holding their attention better. Interesting method!
*laugh* I admit that I consider "dammit, I lost my whole weekend down this series!" to be an endorsement of quality in my work.