Although I don't necessarily agree with where you go with that,
I hope this is not an innuendo, by which you imply that I took a jab at religion (Christianity in particular). I only say this because we have crossed our blades in the past ...on matters of religion.
So in case this is such an Innuendo, let me clarify that I had no such intent. Moreover my post was not insulting to religion in any way. I will repeat (perhaps one time too many in this forum) that the fact that I'm an a atheist, has nothing to do with my views on the game and its deities.
In case I misinterpreted your phrase, I apologize, and let's assume I never said the above.
So... regarding clerics and monks...
I think the root cause is that there is a strong tendency of many players/DM's to filter Cleric through the lens of a Christian priesthood, so that it takes on large numbers of trappings that are very particular to the Christian religion and not necessarily to religion generally.
So for example, there is a tendency to attribute all of the following to the class of cleric generally:
1) They are men of Faith, either at the superficial atheistic level of 'believing in the deity' or the more naunced theistic understanding of faith as 'believing in the benevolence and power of the deity'.
2) They are pious and devoted servants of their deity.
2) They are miracle workers whose power comes directly from a deity or his intermediary as a result of their empowering Faith or faithfulness.
3) They are evangelists promoting belief in their deity and service of the deity.
4) Members of some organized religion.
None of those things in fact has anything to do with the cleric class as described they are just things we think of if we aren't careful when we think of Cleric. It's not that any may necessarily not be true for a particular cleric or particular in game religion, it's that none of those need be true. So that conversely, a cleric in game may be:
1) Men who have through study knowledge of the esoteric characteristics of the deity.
2) Shrewd practicioners of ritual who bargain with and trick the deity or his servants.
3) Magicians whose power comes from using their knowledge to empose their will on the deity or who recieve power from the deity as a result of esoteric bargains.
4) Hoarders of secret knowledge so as to better leverage their power over the masses.
5) Isolated practicioners.
I think you are missing one key aspect of the clerics here. Clerics "pray" to receive the "blessings" of the deity.
And by that "prayer" I understand that there is always "faith" involved in the process.
Whatever that cleric might be, it is only natural to assume that there is some degree of "spiritual-connection" between
the mortal and the deity. Commoners may pray as well, but they have not attained the level of spiritual connection a cleric has.
Specifically:
1) Men who have through study knowledge of the esoteric characteristics of the deity.
This "sturdy knowledge" as you call it, is not sufficient for one to call the powers of the deity. Many historians, scholars
wizards, warriors and rogues even, in the D&D world have thorough knowledge of one or more deities.
They even have thorough knowledge of the "esoteric characteristics" of the deities, as you call them, but they are far from being clerics.
2) Shrewd practicioners of ritual who bargain with and trick the deity or his servants.
3) Magicians whose power comes from using their knowledge to empose their will on the deity or who recieve power from the deity as a result of esoteric bargains.
A cleric who tricks or imposes his will on his deity? Not possible.
A cleric does not/cannot deceive his deity (and remain a cleric of that same deity - just like the Paladin).
As far as the cleric's approach to his "relationship" with the deity he believes in is concerned, there are no "lies & deceit" involved.
The other way around, it is highly possible. The deity (depending on it's alignment and portfolio) may "use" the believers as pawns, and get rid of them once it [the deity] attains it's goals. But again, this only works one way: From the deity to the mortal/cleric. A Cleric is always sincere and transparent in respect to his deity, and it is this sincerity and transparency, one of the components that builds up the connection with the deity. A connection that eventually leads to the mortal receiving powers from that same deity. If the cleric ceases to be truthful, honest and faithful in respect to his deity and it's portfolio, the connection is lost and he ceases to be a cleric of that specific deity. A cleric of Mask, might as well be an assassin, a lier, a deceiver... whatever have you... but NEVER does he use/employ the deity's portfolio against the deity...
The archetype you describe in none other than the Wizard. The Wizard is the one who is able to act entirely on his own, able to defy the very gods and even take their place. A fine example is Raistlin Majere in Dragonlance, Karsus in the Forgotten Realms... all settings and fantasy novels are full of such examples, and it is always done/attempted by wizards, for if there is one class that personifies human greed in fantasy settings, it's none other than the notorious wizard.
4) Hoarders of secret knowledge so as to better leverage their power over the masses.
Again, everything is filtered through the deity's portfolio. If the deity wants it, the cleric has to do it, or at least attempt to do it. If it's not the deity's will, the cleric ceases to be a cleric (and that is the least of punishments!). A cleric won't go searching for a way to control the masses if the deity does not believe in such acts. Even when he does it, he does it because it's the wish of his deity. His agenda, is the deity's agenda.
Ex-Clerics
A cleric who grossly violates the code of conduct required by his god (generally by acting in ways opposed to the god's alignment or purposes) loses all spells and class features, except for armor and shield proficiencies and proficiency with simple weapons. He cannot thereafter gain levels as a cleric of that god until he atones (see the atonement spell description).
5) Isolated practitioners.
Clerics might be isolated from the mortal population,
but they are never isolated from their deities. Whatever they do and think, the deity knows.
A deity knows when a cleric is being true to his beliefs, and that is why it grands him powers.
The same way the deity knows that a cleric is not abiding to its beliefs, and takes the powers away (Ex Clerics).
Western monks are by definition laity and not clergy.
Western monks are NOT by definition laity and not clergy. Western monks are not NECESSARILY clergy.
Whatever the religion or deity, the Monks are people with strong faith and an equal, (if not stronger) "connection to the deity", with the clergy. Moreover there are certain eastern religions where the monks do not differentiate from the clergy.
Even a big number of the Christian Saints derive from Monks, which is to say that they are not lesser to the clergy, in respect to their faith or "connection" to their god.
These are the reasons that it makes no cense whatsoever, that the Monk class does not receive divine powers.