As I understand it, the rock doesn't get especially hot. The hot surface ablates, and the rock underneath remains relatively cool (doesn't have time to heat up).
"Through making the reentry vehicle blunt, air cannot 'get out of the way' quickly enough, and acts as an air cushion to push the shock wave and heated shock layer forward (away from the vehicle). Since most of the hot gases are no longer in direct contact with the vehicle, the heat energy would stay in the shocked gas and simply move around the vehicle to later dissipate into the atmosphere."
From http://en.wikipedia.org/wiki/Atmospheric_reentry#Blunt_body_... (admittedly about spacecraft rather than meteorites):
"Through making the reentry vehicle blunt, air cannot 'get out of the way' quickly enough, and acts as an air cushion to push the shock wave and heated shock layer forward (away from the vehicle). Since most of the hot gases are no longer in direct contact with the vehicle, the heat energy would stay in the shocked gas and simply move around the vehicle to later dissipate into the atmosphere."