Slotted rotors are very common in racing, IMSA Lites Elan's have them, as do most other sports racers where brake use is very hard and heavy. The gas issue is from the past but they still keep the pad surface debris free and serve a purpose. On a street car I'd tend to think they might be useful since rotors often rust up after car wash or rain and keeping that crap off the pads could be useful. Drilled rotors are gay and serve no purpose.

I upgraded the G with slotted rotors (threw out the factory drilled) and Pagid autocross pads, it stops like a beast now but builds up brake dust crazy fast.