The "difference" between the adventurer-cleric and the NPC is not so much when one reads the lengthy and very clear paragraph on the above mentioned page. At least when it comes to practicing what one professes, and gaining the benefits therefrom.
1E is not the godless realm of Holmes, BX or Mentzer (BECM-). With an entire hardback book devoted to deities and demigods, it is clear that "Advanced" is of a different mindset.
Yet, across the boards/forums that I travel, I find so many folks commenting that, though they play/run 1E games, they do not have to deal with deities at all. Well, for fighter types, even magic users and surely for thieves, I can see some logic in that; especially if one intends to be very neutral and agnostic (?).
For clerics/druids?
I just don't see this as the case at all. And my gut feeling is that, DMs that do not hold a tight rein on clerics and the source of their powers, are-- invertly-- BX, Holmes players at heart. But just don't want to give up all the goodies associated with 1E.
That's fine.
Homebrewing has become so rampant that, we have succeeded in transmorphing things to mulligan stew. Only, the ingredients are not shared from house to house, so one does not know exactly if they're going to like visiting the Joneses, when the Mrs. dumps tons of garlic in her stew. (A little awkward, but you get the drift)
So, in godless worlds where clerics still get all their power without behooving to anyone, aren't they really just a case of watered down fighters, but with some kick ass spells? Or, worse, walking medlabs dragged along for their CLW, CSW, CCW...?
I am digressing. Big shock, eh?
Your thoughts....(and keep them clean!