In this case I don't think it really matters. No one says "my car is fine, it's just rusting not biodegrading". What matters is that the car is disappearing right before your eyes through natural processes that could have been prevented with normal maintenance.
Wood, when properly taken care of, lasts forever. Steel, when properly taken care of, lasts forever. Each of them will degrade without proper maintenance, and oddly enough they both have basically the same maintenance needs. Keep them dry, otherwise oil them occasionally.
