I strongly agree that drilled rotors are just for looks and do little or nothing for brake performance. As already mentioned, the holes provide stress risers for the rotors to crack and indeed they are much more prone to cracking.
Drilled rotors, however are not difficult to machine. If someone says they would rather not machine them it is probably best that they don't try. I have machined many. It is best to take a lighter cut than you may want to if you were machining plain rotors. Some companies that drill rotors claim that they countersink the holes deep enough to somewhat reduce the cracking problem as well as make them easier to machine.
