Saw this posted on a mountain bike forum:
"Brake fade isn't caused by boiling brake fluid, it's caused by the brake pads becoming extremly hot and giving off gases, these gases become traped between the pads and rotors when one tries to brake, keeping much of the pads from touching the rotors, this is why braking power is reduced."
Obviously the first part of this guy's comment is wrong, but I've never heard of trapped gases causing fade...a fancy way of describing glazing, maybe?