These guys read their semiotics, but they didn't limit themselves to linguistics. Sure it's interesting to ask how words stand for real things (or, in fancy terms, signify). But it's even more interesting to get at how narratives create meaning—what are the underlying structures of literature? And since all society and culture is made up of signs and codes, they don't limit themselves to the classics. They believe in analyzing magazines, ads, movies, fashion, hairstyles—whatever they want to write about, really.
Saussure helped found semiology and structuralism, and he's still so big that you have to label yourself in relation to him—are you post-Saussurean? Non-Saussurean?
He could do the linguistics with the best of them, and he's also our true-blooded structuralist. He broke all types of communication down into a few basic modes—from informative to poetic.
Lévi-Strauss took structuralism from its roots in language, and brought it to anthropology. If language has a grammar, and stories have certain underlying structures, then maybe entire cultures do, too. (Like how so many different cultures have similar myths and folktales.)