A concerned reader sent me this distressing news: Nefarian is no longer immune to fire damage. Shocking, I know.
Gameplay vs. Simulation
Using wording shamelessly stolen from Nils we can see that what is happening here is a weakening of simulation in favor of gameplay. It is easier to balance the encounter, and gives classes more options in their talents, if one tree of magic is not blocked. It also doesn't make much sense that a powerful black dragon is vulnerable to fire. These are the same dragons who come from eggs stored in a cave where lava is all over the place and whose mother, and/or wife, and/or sister, since dragons are weird like that, breathes fire all over the damn place, including on the eggs. His distant cousins under Wyrmrest have a tendency to throw waves of lava around with no damage to themselves. Fire just is not their main problem.
At an extreme I could see it. I'm sure if Deathwing started spewing fire they'd get toasted. Just like we can imagine that a sufficiently powerful mage could damage Malygos with arcane damage, but that bridge has been crossed, burned, and washed away. Not as if that fight demonstrated much gameplay-simulation tradeoff since it didn't do either very well.
I replied with this line from Game of Thrones: "He was no dragon, Dany thought, curiously calm. Fire cannot kill a dragon."
Not at all a waste of time
I'm being sarcastic. Changing the fire-immune status of a boss who has been old news for three expansions was a waste of time. It is an attempt to balance content that doesn't need to be balanced because it's already trivial.
It's all connected and I can prove it because I'm saying it very loudly
Dragon Soul comes out or came out or something, I've not been paying much attention, and people say it is too easy. Dragon. And at the same time, another dragon is retuned. Don't you see? The devs wasted all their time testing Nefarian to make sure he's balanced for level 85s soloing him for hats rather than testing the new raid. Normally I'd make a chalkboard drawing some dragons and an arrow or two, maybe with an exclamation point, but this is far too serious for mere chalkboards. Instead, I'm going to just leave you with this chilling thought:
P.S. Someone please leave a chilling thought in a comment; I'm coming up blank.