Even just the one running thread of "propane and propane accessories" through King of the Hill paints a deep satirical portrait of middle class salesmanship, an equal to (if not a successor/better) "Death of a Salesman". I'd even possible put it up against Vonnegut's Breakfast of Champions for levels of grim pathos and determination despite broken systems that don't allow for advancement while claiming that they do.

All of that seems like hyperbole perhaps, but it's an admirable trait to King of the Hill that it can inspire such questions and discussions... and that's just one of the many long-running satire threads in King of the Hill.