Quote Originally Posted by Bohandas View Post
It;s strongly implied that that was not the most expedient and pragmatic solution even in the case where he did it; that it took a lot of cunning, trickery, and mad science and was motivated by anger and a sense of baroque contrapasso, rather than by quickness or practicality
And much about how the Doctor works is governed by aesthetics (especially dramatic irony)--the punishment must fit the (attempted) crime. It's a basic rule, not of the universe, but of the Doctor. And those rules are more binding on him than mere physical law (which he tramples on regularly).

In general, when dealing with such things there's always an unspoken law. It's unspoken because trying to explain it would ruin the fiction (by being verbose and boring and something that very few people actually care about). It's plausible coherence that matters. Lots of things work under very controlled situations that just don't work in other cases. And for magic, especially, the mental is more important than the physical, the perceived more important than the actualized.