Feets does speak truth to his claim. The reason why rotors that are drilled tend to fail quicker than rotors that are cast all has to do with the grain structure. When you drill into a rotor, you are drilling through the grains and interrupting the grain structure (i.e. around the holes, the grains are going to be smaller due to the material you removed vs. the rest of the structure). The rotors that are cast with holes in the casting are going to have a fairly equal grain structure throughout the whole structure (including the area around the holes). That's as much detail as I can throw out at the moment about materials with 3 hours of sleep.