You know I wonder if it has to do with Harry being Warden, and you ending up on DR if you conjure his name. Perhaps he shares a connection with Alfred that grants a layer of protection.
I wouldn't doubt it's something similar to that effect. Certainly the Warden would need some sort of protection from evil primordial beings. Otherwise how would he be capable of capturing them and bringing them to Demonreach.
Plus Mab as the Queen Bee fighter of Outsiders, might give her key champion some protection against them.
Plus Soulfire from Uriel who is himself damn near close to a Primordial being.
Plus.. you know... STarborn. Definition of a magic user who can fight against Outsiders.