No, they're totally right about the ridged heads. Think about when the alien takes out Dietrich in Aliens - you can't see it above her because its head blends in. With a smooth head, it'd stand out against the hive. And the smooth heads let the alien blend into the ductwork on the Nostromo's shuttle, or into the plumbing on LV-426. Whether it makes biological sense, it is still how the looks were used in the movies.