Yes drilled rotors were made for a problem in race cars which no longer exists. Look at the F1 cars brakes now days and there are no drilled holes or slots. Old pads made a lot of gases from the glue that held them together and these needed to be vented out in order for the breaks to preform. Drilled was the most effective but had the side effect of producing cracks so after each race they would need to be inspected and/or replaced. That's not reasonable for day to day use. Slots didn't crack and were better then nothing at all.
But today modern pads do not have much if any issue with gases being formed. F1 cars and other race cars don't use anything because it is not needed and holes or slots reduce the overall braking surface.
My advice is get the best 2 piece brake and good pads. Slots and holes are just for appearance.
http://bikehugger.com/post/view/formula-one-for-bikes