It is my understanding that it has more to do with adapting to Japanese video game content standards. Games that involve direct melee cutting incur higher ratings-specifically, "D" or "Z," the equivalent of an M or AO game, respectively, in the US. By representing a sword attack as a magical slash it bypasses the sort of actual cutting a sword attack usually does, thus somehow becoming less violent in the eyes of a censor. This is akin to why in Germany enemies are portrayed as aliens/robots and have green blood.