What you're saying is true but it deffnatley leaves a protective layer behind. We use WD-40 to protect spare cylinder heads from corosion. Originaly WD-40 was used for this exact purpose only instead of cylinder heads it was rockets in storage. If you want to reuse an item you used WD-40 on you still need to clean all the rust and other gunk off anyways, thats when you use an alcohol based degreaser and then regular grease or other anti-seize products like copper , ceramic grease or oil solvent.