They don't count as magical, but the undead (specifically VC) have a ton of units with the regen rule. The addition of the new mortis engine only makes this worse, as it adds +1 to the regen score of any undead within 12 inches (maybe it's just 2d6, can't remember). Flaming banner lets you rip right through their saves.
For TK is is nice because their characters are often flammable.