Maybe that's because spell tactics are a subset of tactics?!
Drain Magic cancels Judgement of Verena which is enough to me to justify the adding. Moreover it cancels most of the fancy cards like Black Horror, Sacrifice to Kaine, Chain Lightning, Plague Bomb. And it even cancels attachments.
Well I knew that (in regard to the first part), point was that there are still two times more non-Spell tactics. I did a quick mental tally on the cards DM would normally work on in the decks around here and Dwarves are barely affected at all, while HED takes care of Reclaim the Fallen and My Life For the Hold. Empire's main Tactics, Called Back and Forced March are again immune to DM, although JoV is affected, as is Manaan Take You (no Chain Lightning for Empire). Chaos is probably the most affected, but then again, they have such an amount of Tactics that losing one is like a drop in an ocean, not to mention all their units with damage or other actions (that even HED doesn't touch). Against Orcs DM is pure development-fodder, HED gets Pillage, Troll Vomit and Waaagh. DElves are close to Chaos with their Spells, but have Tactics in lesser amount , although DM doesn't touch We Need Your Blood or either of the unit-stealing (from opponent's discard) Tactics. Only Attachments DM would get would only happen in a HElf vs HElf matchup, but only have one deck for each race so that can't happen . I think above is a reason why DM for me went right into the storage box after opening the BP.