The Simpsons live in what has been called a "rubber band" universe. Things will get stretched out in one episode for the purpose of the plot, i.e., the family can easily afford a trip to Brazil while the next episode they barely have enough to afford a new motor for their refrigerator. Same goes for their hair/skulls. In this Halloween episode and others, the children are shown with pointed skulls. In an episode where Santa's Little Helper needed surgery, Bart had to get a cheap haircut to save money and it shows him nearly bald with no spikes.
TL;DR They writers use pointed skulls to show who they were.
TL;DR They writers use pointed skulls to show who they were.