As this seems to be a running theory, I figured I would post to clarify.

There is absolutely nothing wrong with the Demonologist (or Necromancer) magic ratings. You will notice that the buff from either of the specialized fire/electrical/unholy/cold buffs added to your base magic rating will equal your resist rating, or any other "target" rating for your level.

For instance, the target at level 80 is 317 ratings, which is achieved with the base value + the buff value from either school rating buffs. (Obviously, if you have Archmage, the buff will also apply to both schools instead of just one.)

So, in the end, it is Magic Rating + Specialized Magic Rating vs. Resist Rating for the purposes of combat calculations.

Additionally, no stats were intended to apply to magic (or attack) ratings, and this was simply an error in the tooltip text until it was corrected last week. Intelligence increases magic damage dealt, not magic rating.

Fruthermore, Magic, Attack, Defense, and Resist ratings do not apply in PvP at all, to provide a more even playing field for all players of all level ranges.