Not really true. It's illegal to offer engineering services to the public for projects not suitable for instate commerce unless you're a PE. If a hypothetical project could possibly be built in one state and sold in another, you don't have to be a PE. Professional Engineers usually do roads, bridges, footings, big earthworks, stuff like that. Most Civil Engineers find that they have to be PEs to even hold a job, while almost no aerospace engineers are PEs. Turns out that airplanes can cross state lines pretty easily. Electrical Engineers who are PEs are mostly found in electrical utility design and construction.
Different rules apply in Canada and probably every other country. "Engineer" is a trademark in Canada, and the Canadian PEs protect their turf through trademark law.