I don't think I'd want to visit a Daventry where the "magic mirror" is the one with cocaine residue on it.
Or the narrator has to inform us, "Alexander's dime is not really enough to purchase the 'dime bag' offered by the skinny young peddler." Or Cedric says, "Look out, Graham! The brown acid is cut with stryyyyyyychnine!"
As much as King's Quest can sometimes verge on self-parody, its intentionally family-friendly universe is part of its nature. Classical fairy tales are often metaphors for darker themes, but spelling those themes out in detail wouldn't feel right somehow.