Physical vs Magical, implementation in this game.

[RitsukoSonoda]

WoW had vague elemental resistances, but it doesn't compare to Ragnarok Online's or FFXI's elemental system. People keep mixing them! Resisting an element is not the same as taking either twice (x2) the damage, half the damage (x 0.5) or zero damage from a specific element. I wish FFXIV would reincorporate such features, but apparently it's too stressful.

Not really stressful. Initially I'd say it was culling to appease non RPG players in the belief they wouldn't be able to handle such mechanics. At this point they wouldnt be able to implement elemental resistances like that without doing a complete ground up rebuild of a number of jobs already in game.