I saw a few - in some cases, they were carrying backpacks, which seemed to exacerbate the problem (I've got a photo of one chap).
Other people just looked completely knackered. An Aussie and I were riding behind an old geezer after Villaines on the way back, and we checked he was OK at the top of a climb, but he simply gave that French shrug and carried on. Watching him descend was terrifying (and we did watch him - we were keeping him where we could see him), since he was mainly made of sticks and spit, and he'd probably have snapped in two if he'd come off. He reached the next village, had to be dragged off the bike and dumped on a table, where he went out like a light.
Core strength issue?