It’s about the line between what gets protected by patents and what gets protected by copyright. The rule is basically patents protect function, copyright does

It’s about the line between what gets protected by patents and what gets protected by copyright. The rule is basically patents protect function, copyright doesn’t. If the specific design of a windshield wiper blade was protected by copyright then its patent would be pointless. Therefore patents essentially invalidate copyright where they apply. People often hate software patents, but a 20 year window expires on anything built before 2004.