The whole rift between the "god" and "powerful being" in D&D came from the perspective of the Judeo-Christian mythos. In Judeo-Christian belief, all "good magic" was simply the power of God channeled through a prophet or saint or the power of God Himself in Jesus Christ. In non-Christian belief, in general, magical powers were not so much *granted* by the gods as they were *taught* by the gods, as the mysteries and triths of the universe. Witness the inherent superiority of Moses' snake, which was the power of God against the common magic of Pharaoh's wizards, or the power of Jesus and the various saints to raise the dead and heal the lame, which came not from any knowledge they had, but from their piety and the beneficience of God.
The cleric class in D&D, however, was not originally based on the non-Christian priests, it was an amalgamation of the early Christian saints with the crusading clerics of the crusades, and thus, coming from a Christian sort of perspective, the "magic" they possesed came not from their own mastery of the various mysteries of the universe, but instead directly from their god... which was a Christian concept.
Thus, when TSR backed off due to negative publicity about demon worship and so forth, they divested any "god-like" beings that might be construed of as being devils or demons of having the ability to grant divine spells... even though the various "pagan" gods continued to ahve the ability to do so. As various tales from those days at TSR seem to indicate, this middle ground that was chosen could well have been as much from upper level management ignorance of magic, religion, and history as it was from intent. Witness the changing of the names of the outer plane from Hell to Ba'ator and other easily recognizable (to American Christian ears) names from "demon worshipping" stuff... yet they kept various more esoteric names untouched, such as Gehenna (which is nothing more than Latinized Hebrew for "Hell").
Anyhoo, this kind of dichotomy — "things that could be readily Christian demons and devils" not having spell-granting abilities versus "pagan and heathen gods" having such abilities, kept throughout most of the TSR period. Then, in general, WotC really didn't care once they acquired the property, as the ownership was a bit more aware of what was really going on, and unconcerned about fundamentalist backlash (which had long passed D&D over for far more fertile fields of endeavor).
One little oddity that remained from that era, though, was the use of the term "Immortal" and the whole developement of a different kind of divinity in the BECMD&D setting of Mystara. It being the "extreme intorductory game and setting," it eliminated ANY reference to gods whatsoever, and made the "gods" powerful former mortals who simply had a lot of power... though there were older Immortals who could never remember being mortal, and there were the mysterious Old Ones, beyond even them.
And then, of course, Forgotten Realms and Dragonlance evolved the concept of the High God, who was to the gods as the gods were to mortals, thus further pushing the whole kit and kaboodle further away from any sort of connection to "true divinity."