Part of this thread really is about creation myths. Where (and when) did it all start? Why is the multiverse what it is today? And who exactly is running things? Is it really the gods?
While Spelljammer is often derided as a "joke", and yes, a freely admit that some of SJ was played for laughs, there was alot of thought put behind it, and how to integrate it with the rest of the DnD multiverse. And the physics of SJ are quite a serious attempt at crafting a new type of gaming environment. Why does DnD "space" need to be like real "space"? It doesn't! With magic, and dragons, and gods you can shake hands with! But many people hate SJ exactly because it does not resemble "real space". Hypocritical if you ask me. Open-deck ships with gravity are much more DnDish then the alternative necessary without SJ's unique physics.
As pointed out already by Arnwyn, the idea of crystal spheres in the phlogiston serves quite nicely to isolate individual worlds and their gods, yet provides a means of getting from sphere to sphere without spending centuries in transit. So where does this all start? The spheres must necessarily be very old, yet gods change. IMC, the "present" gods therefore had nothing to do with their creation. They may delude their followers into thinking they were the "creator gods" but nothing could be further from the truth. Many people choose to use the boring idea of present gods as creator gods, an idea that I personally do not like.
To quote my website, the average DM's creation myth goes as such: Anthropomorphic God A pops into existence out of the firmament. (Here I stop reading). God A gets lonely and creates God B, either by budding, or shaping out of clay, or "poof... God B", or some other tired cliche. God A pops God B, producing children Gods C, D, E and F. They fight amongst themselves, pop eachother, divvy up spheres of influence, create planes for homes, create mortals, perhaps produce another generation of young gods. The End. All these gods have names we recognize. All these gods are still around.
Boring.
IMC, as with other who have commented in this thread, gods are merely another rung on the ladder of "beings". They are far more powerful then mortals, and immortals such as fiends, yet they are still just critters. IMC, the Athar (from Planescape) are correct. There are beings higher up the ladder as well. Ultimately, at the top, are the beings responsible for the shape of the multiverse itself. While it is a rather long read (MUCH too long to post here), I point to anyone interested in my theories to my "Life, the Multiverse, and Everything" webpage in the "Epic Mysteries" portion of my website (which I just finished rewriting and expanding) at
http://melkot.com Hmmm... let see, the direct link would be
http://melkot.com/mysteries/multiverse.html
On that webpage I explain the formation of the Multiverse, and how the rules of physics and magic came to be - accounting for everything from ethos (law, chaos, good, evil) and how the outer planes came to be, extradimensional space, differential time across the planes, sentience, matter and magic energies, and, pertinent to this thread, what the gods (Powers) are and where they came from. I also describe the beings that are actually at the top of the Multiverse food chain.
As for the present-day gods themselves IMC, they are merely the most recent in a long line of gods, the names of the previous generation wiped out by the propaganda of the next. I consider that their energy for sustenance can come from a variety of sources. Some derive energy from their followers like divine parasites. When those gods lose their worshipers, they starve and may eventually die (their husks banished to the Astral). Other gods derive their energies from other sources. For example, Boccob derives energy from the flow of magic itself, hence as long as wizards are casting spells and creating magic items, he will live on and hence is "uncaring" of any worshippers. Others may exist by merging with or feeding off of planes. IMC, the current gods are relative newcomers, and none of them are responsible in any way for the formation or modification of the multiverse, any of the planes, or any pieces of it. Oerth, Faerun, Athas, Krynn... all existed long before any of the gods who claim those worlds as their own, and will exist long after the present gods are gone and replaced.
Denis, aka "Maldin"
Check out the ton of other cool Edition-independent stuff on my website, from new magic items and spells, new game mechanics, and loads of juicy Greyhawk goodness.