That's not true at all. My airplane, which is a Part 23 certified, factory-built aircraft that was made by Grumman-American, has numerous fuel lines running through the cockpit, and none of them have any fire protection on them, not even firesleeving. They are made from aluminum and copper, which are not considered intrinsically fireproof. That's also the case for every Piper and Cessna aircraft that I have worked on, which are typically older CAR-3 certified designs.