This scene is a great example of the mystery behind being hit. Throughout the game you face monsters and soldiers that shoot you, stab you, light you on fire, pound you into the ground etc etc and yet you survive to fight another day. You could always look at the giant ice spikes as just a way of taking out a great amount of HP.

This is looked at in the same way as someone saying "Why can't you just use a phoenix down on a character who's death is plot related?".