These tables are correct. The warriors in the army list are a mutated species, they are not the basic warrior profile. E.g. termagants are pre-modified too. If you create your own species of 'nids you use the very basic profile of a subspecies, in this case the warriors are S4, but cheaper. If you do not want them to be S5 for any reason, then you do not need to spent the points of this upgrade on them, as it already happened with the warriors in the army list.
jwu