because they blur into each other in ways that don't have externally-visible consequences.

Not true; look at polarix's top-level comment.

A generalization of that idea is that torture represents, at minimum a causal chain with the torturer as the cause and the victim as the effect. Therefore changing some parameter of the torturer should result in some change of parameter of the victim. But if you're just loading frames from memory, that does not occur. The causal chain is broken.