I've no problem accepting that. And while I'm sceptical of In Bloom's description of the UK IMC's workings, even taking both points at face value makes no difference to my argument.
Indymedia UK has a hierarchy - active editors, list participants, ordinary users, to give just three of the more obvious concentric circles. It also involves the use of authority, where with whatever level of mandate, some people decide on rules and then enforce them over users. As I said I've no problem with any of that, although I think Indymedia UK's editorial teams use of its authority is pretty fucking daft. The only problem here is a conceptual one for (some) anarchists, who regard hierarchy and authority as inherently bad things.
It is in my experience quite a common trait amongst anarchists. Start by defining certain things as bad (authority, leadership, state, hierarchy). Then in a more or less skillful manner move the definition so that authority anarchists approve of becomes not-authority, hierarchy anarchists approve of becomes not-hierarchy. And words become meaningless except as swear words or political insults.