THat's true, but most of the helmet is not supported above a certain point by the **** sides...about the jaw or cheek line. The driver also needs to turn his head during the turns (checking mirrors, looking around the corner etc).
Finally, it's during the braking where they have to keep the head up against the forward pull during the incredible deccelaration (also close to 4 G's initially...drive has to modulate the brake as the downforce & airspeed drops during braking...otherwise they skid off the track).