[91 Celica St]

Yes they do. But, they also reduce the amount of heat that the rotor is able to absorb which is what leads to brake fade. Think about this. The rotors main job is to absorb the heat created by the pads. Big Brake kits do this by adding mass to the rotor, ie going to larger diameter, thicker rotors. This allows repeated hard stops without cooking the brakes. When you remove mass from the rotors, ie crossdrilling, you reduce the heat absorbing properties of the rotor. So, it has less ability to absorb heat from the system which makes the rotors overheat faster. And then, as you stated the heat get dissipated by the "cooling holes." Which causes uneven cooling around the holes vs the rest of the rotor surface. This leads to cracks with repeated use. Some drilled rotors are better than others. Porsche actualy casts the holes in their rotors. This makes them a little more durable but, they will still crack before a solid rotor.

All rotors will crack with hard use. But, why do something that will make them more likely to crack? Crossdrilled rotors will crack before slotted rotors. And slotted rotors will crack before "regular" rotors. I personally only use regular rotors on my cars. Have you ever seen what happens when those tiny stress cracks get bigger? Can you say multi-piece rotor?