Frankly, I think it's possible to overplay this argument, just as it would be rather silly to claim that the use of the image of a human skull as a symbol of death is utterly arbitrary. But in everyday terms, I think that games and settings have reputations and practices associated with them. You don't have to play Game X differently from Game Y, but if you're invited to play a game and you've never gamed with the people involved, the choice of rules and setting are going to condition your expectations. I even think the expectations of different games will be positively correlated across the population. And it doesn't matter if this more a matter of "pure reputation" or if it's actually connected to the mechanics.
When it comes to settings, I think the connection to expectations is at least as strong. Announce a campaign set in Hârn and people will generally expect a fairly naturalistic kind of low fantasy. Set a campaign in Mystara, Greyhawk, or Forgotten Realms, and I think people will expect a more high fantasy game, and they'll be more in tune with a kitchen sink style, up to and including things like extraplanar adventures.
The upshot of all this is that if you're casting a wide net looking for players among existing RPGers, a known setting could be a good way of attracting people with common interests. But if you really want to GM your homebrew setting, and it's out of the mainstream and a little idiosyncratic, then maybe publishing it is a good way of advertising it. The world may not need your POD or PDF, but you need players, right?
So now I've ordered my priorities. There are already a number of published settings I'd be glad to GM. Some off the top of my head: Talislanta, Chronicles of Future Earth, the medieval Baltic as portrayed in Crusaders of the Amber Coast, Jorune. Still, there's a homebrew I've had in mind for a long time, and getting it out there could have utility beyond pure vanity.
At least, these are the thoughts motivated me to look into ways to organize and present a setting, both as an end product and as a process.
I've noticed that a lot of people use wikis to manage their campaigns, so to start with I've found some free wiki services. These are general-purpose wikis that are also popular with RPGers:
Next come wikis, or wiki-like sites, that are expressly provided for RPGs:
Then a general-purpose service that lets you create websites:
A couple pieces of software that use a wiki-like structures for local organization of information (but not, apparently, for publishing)
Websites devoted to online roleplaying, which include tools for displaying campaign information:
And finally, a thread and an article related to this topic, from which I gathered much of the information above:
Feedback on any of these tools would be welcome. (We'll see if anything comes of it for me, personally.)