Pure speculation here, but if what you were told is true about 1/3 of engine cost being liability insurance costs, I would expect a larger proportion of airframe cost would be insurance cost related. The aircraft manufacturer may be found liable for any component installed in the aircraft, including any airframe or engine discrepancy resulting in mishap! The lawyers would go after the big game (Cessna, Piper) then hunt rabbits (Continental, Lycoming, etc.) incidental to the original suit.
