I can see some differences very easily. One major difference between most D&D gods and religions and a real world God and religion
is that of subversiveness,
and a Cosmic Plan.
For instance it is very easy for me to imagine, and believe, in a subversive Cosmic Plan of God, one which basically overthrows the nature of the world in which people live, and which has all kinds of secret and covert components. That is to say God has secret plans for the world, which the followers would find hard to imagine or conceive of, and hard to fathom correctly (though they might very well understand or even just intuit the basic implications of the plan). Because God would have no "real interest" in the world, per se, but rather it would be a stage, or construct upon which to play out his Cosmic Plan. But he has no real desire to see the "world" (as it is currently construed, functions, and is imagined) or the world system continue indefinitely. He has other things in mind. Because of this he would operate quite differently, even towards and in conjunction with his followers, than he would if he did not have such objectives.
A D&D god however is far more likely than not to be "a part of his world" (rather than existing independently of it) and therefore his plans would be objectives of intrigue, rather than of a secretive, covert, Cosmic Nature. A D&D god is "of his world" and is therefore intimately tied to it, and the fate of his world is to a large extent his fate as well. Yes, some gods, especially evil ones, might want to undo the world even, to a certain extent, or kill off all others deities, but mainly to gain power, than for other reasons. The Greek gods for instance were prone to much intrigue, playing their worshippers and followers in games of personal interest, for entertainment, out of basically human desires of lust (Eros) or greed or revenge, or for the sake of power. (The Trojan War is an excellent example of the same pantheon of gods engaged on different sides for different reasons. Many were involved in the war directly for personal aims, or to accomplish personal objectives, but none, not even Zeus, had a long-term Cosmic plan for the outcome of the war, or what it would ultimately achieve. In truth they did not know what it would achieve because few of the gods, Apollo could to a degree sometimes, could foresee the future.) But none of them could be said to have a true Cosmic Plan about the Cosmos, or life in general, or human life in particular. They weren't even really creators, they were usurpers who had assumed power from far more cosmic gods and forces far older than themselves.
And that was true of almost all polytheistic pantheons. Creator Gods and gods were very different things and had very different interests and motivations and objectives. Because a Creator God is not limited or absorbed in time as a god is so limited or absorbed. You can pray to a god, "what is your plan for the future?" but the god really knows only what he wants to happen, not what will actually happen. A Cosmic God with a Cosmic Plan, well, in that case you pray to him to try and help you understand what the future will be. Because he is not limited by time or the world, he stands beyond them, even when absorbed in them.
So as far as differences go, then I'd say gods are full of intrigue, but they have no real
"End-Game."
But real God, especially a Creator God, he would very likely have an ongoing objective, even if that wasn't readily apparent to anyone else, or what they anticipated. He'd likely have a real objective, or set of them, far greater than sectarian interests or even worldly interests. He'd have a "Cosmic Plan" and so he'd operate completely differently than any god.
And any religion built around a God with a Cosmic plan is also going to be very, very different, and operate very, very differently than that of a god with individual and immediate interests. A god can to a certain extent control space, God would control, even if he choose to do so in a completely unforeseen or unanticipated manner, both space and time.
A god will have tactical interests. But he cannot know the ultimate fate of the world, only what is prophesied or assumed about it.
God on the other hand would have strategic interests and what is prophesied would be only a sort of assumption of his real objectives.
3) One that designers should incorporate into D&D more is different churches, sects or religions around the same God(s) or principal. Think about how many different Christian sects there are. And how distinct their visions are of how to serve God. Or you could even have three different religions surrounding the same God (as you have with Christianity, Islam and Judaism)-- though this is harder to do because you really need a good explanation for why one group follows this prophet or believes another prophet to be divine.
I like and agree with that idea.