While I agree that dc/dc supplies are a good idea for electronics I think it is a stretch to imply that they will protect equipment from a lightning strike. The insulation values are at best 2500V. A lightning strike will jump across some impressive air gaps to get to ground. The amount of energy in a strike can be impressive, even melting sand into dissipating tentacles of glass. Where isolation come in is mitigating voltage drops from large loads on board and any electronic switching that may cause voltage spikes on the DC system.