I noticed the same thing, but wondered if they had removed the helmets on the final ascent - appears to be the case:
"Stage 15 will pass the spot on the descent from the Porte d'Aspet where, in the 1995 Tour, (correction) Motorola's Fabio Casartelli died when he crashed and hit his head on a low concrete wall. The white jersey competition has since been named the 'Souvenir Fabio Casartelli' in his honor.
Perhaps the greatest legacy of Casartelli's death is the UCI helmet rule, which has gradually been strengthened to the point that this year, riders can be fined for riding without helmets at any time during the race (last year, they could remove them on finishing climbs)."