actually its debatable if cross drilling or slotting actually has any benefit.
its a pros and cons sort of deal. but its proven that regular flat rotors have the potential to offer more than enough braking power
its a back and forth argument.
I've heard the same thing on plain rotors without slots and holes, some are just as good as the vented rotors.
Seems like Jaguar has some proof of them making a difference enough that they put them on their cars.