The S model rotors came drilled from the factory.
One of the often mentioned benefits to drilled rotors is to allow venting of heat/gas that builds up between the pad and the rotor to escape into the holes.
The only real downside to drilled rotors is that they can ultimately grow cracks that emanate from the drilled holes. When this happens, the rotor needs to be replaced (regardless of thickness). Lower quality rotors or extreme heat from track driving will exacerbate the situation. In normal street driving with a high quality rotor, this shouldn't be of any concern.
Slotted rotors (or dimpled) are meant to have the same venting benefits of drilled rotors without the risk of cracks. Thus, a cheaper rotor can be utilized without concern from high heat.
For regular street driving, it probably doesn't matter which style rotor you use as long as they are a decent quality.
For reference, this is what my drilled rotors look like after many repeated hard core track/race days...
Threaded Mode
