So, if the posters are free, what’s the actual protectable intellectual property in these companies? How do they differentiate their product? What’s to keep someone else from, like, offering the Nebraska minimum wage poster for 5¢ less?

Companies don’t reward you for masking dysfunction. They rely on it. They reward the person patching it up with even more responsibilities. Not the kind that come with a promotion, but responsibilities that come with with more fire drills and more late nights.