On the nature of the Blandford-Znajek mechanism
  It is widely accepted in the astrophysical community that the event horizon plays crucial role in the Blandford-Znajek mechanism of extraction of rotational energy of black holes. In fact, this view is a quintessence of the Membrane Paradigm of black holes which suggests that the event horizon, or rather the so-called stretched horizon, is similar to a rotating conducting sphere of finite resistivity. In this paper we argue that this interpretation is rather misleading and the proper explanation of the Blandford-Znajek mechanism has to be sought in the properties of the ergospheric region of black holes. 
S.S. Komissarov