I think you misheard. Some cough syrups do work. the only thing I've heard about cough syrup facts is that cough syrup doesn't work by coating your throat so it is okay to have a drink of water after you take some. I never was allowed to when I was little, and I hate the taste of cough syrup.
I've had cough syrups actually work. They also dilate my pupils and give me cold shivers. That's why I prefer the suppresants - things with menthol or pectin in them.