A Sphere of Annihilation is a device of ultimate horror, an artifact with the ability for near unlimited destruction. It also is frequently used by evil wizards in their lairs.

I think whatever wizard creates SoA would think to cover them in a few spells to prevent 'nonliving, nonmagical air' from rushing in.

On the other hand, Acererak is undead... Wait. I got it. To add to its deathtrap-ness, it will be drained of air if I ever run it.

DM: You stand for the entrance of the ToH. Two large sealed doors with skulls carved into them prevent access.
Players: We open them!
DM: The moment you start moving the doors, air starts rushing in. You are all dragged along, past several traps (roll me 45 saving throws, please) and through various doors and secret passages which all have been opened, probably for this exact case. The air current drags you into a small black sphere it is flowing in. You are dead, please make new characters.
Players: