My friend recently tried to say that wave serpents cannot tank shock because they are skimming transports and pointed out the section on tanks: unless the vehicle "type" is 'Tank (Tk), then they cannot perform Tank Shock or Ram actions (page 92, first sentence). He was aghast when I showed him the Eldar codex entry for the serpent.
This further confirms in my mind the favoritism that was meted out to the Eldar in their codex, when the wave serpent was made to be a Tank, Skimmer, Fast, and a Transport.