[Vedran]

True. Spells casted during cutscenes are not those you can memorize (imagine Irenicus casting all those killer spells at thieves who succeed their saving throws).
For example, browse spells with Shadowkeeper: there are six Flesh to stone spells, seven dominations, ten dispels, twelve lightning bolts... These are used by different creatures (golem's haste is not the same as wizards or Mazzy's) or in some scripts (Irenicus spells are more powerful than standard ones).