Death cult serving Sithis may have never changed, and that is all just fine. It is not so much a question of whether or not they are a death cult (they clearly are), but of the kind of organization and structure of the cult, and whether the structure and function of it are plausible, realistic, make sense. Multiple listeners for the entirety ot Tamriel, in differing provinces, with professional discipline and practice, would make sense. Could even be one supreme head-listener conntected to Night Mother would have priority, I suppose. Still, there would have to be a realistic chain of comand, a realistic internal order, and some semblance of mature professionalism. But logistically, a single listener for an entire world with a bunch of psycopathic juvenile-minded followers is not really a credible DB.
(edit) Although, as I think on this more, maybe the single listener thing has some plausibility after all. There can't be that many Black Sacraments performed, even in the whole of Tamriel. It is not something that most people would do. Assassination is not the most common of activities. So a single listener actually could easily receive the information from the Night Mother, and pass it along. And this also fits with the in-game literature and lore -- see here http://www.uesp.net/wiki/Lore:Dark_Brotherhood
(Especially note the books section at the bottom, with the accounts of DB and Night Mother history.) Nevertheless, a solid organization and professionalism are still needed.
Moreover, in Skyrim,
Spoiler the plot has us starting with no actual listener at all. If this is the case, then there is no way the DB would know who is doing the Black Sacrament, since it is the Night Mother who gets that info and passes it on to the listener. No listener, no knowledge of Sacraments done, no contracts actually made, no DB.
So the Skyrim premise and plot are still completely illogical and faulty, regarding the DB.