Thing is, you're both right, and you're both wrong (Sprig and Firemeboy). I can see where putting it on the web--IF your publisher doesn't object, but as an editor I sure would--MIGHT draw readers, but for the most part, people just don't like to read book-length pieces on a screen. I've only done it before for one person, and that was for a good friend. I now print out that same person's manuscripts and read, because it just plain makes me physically uncomfortable to sit there reading like that on a screen for so long.
So, you have a point that if they read a bit of it online, they might go buy the book. That's where sample chapters come in, though, not full-length books. Hook them in and get them interested, then they'll go to the store and find the book. But of all the people I know in real life, I don't know one person who's gone looking for a book to read online.
As far as Sprig's point about you being the one doing all the marketing, I think what he means is that when you have the backing of a publisher getting your books into the bookstores, you can then do signings, bookstore appearances, school talks, writing conferences, and so forth. It isn't just the clerks doing it, it's your physical presence in the store, too. And your physical presence in the store is facilitated by publishing through a publisher.
Now, you're in a niche market, so a lot of these kinds of things are tweaked with the specialized market of Utah. But if you ever want to reach a wider audience than Utah, you darn well better be sending your manuscripts out to legitimate publishers, because it's a one in a million chance that you'll get that many readers--whether they buy your book or not--without the marketing of a publishing house to back it up. Even the little books, the ones that aren't expected to do well, get put in Random House or HarperCollins or whoever's catalog, and booksellers use those catalogs to decide what's going to go on the shelves. The distributors also use those catalogs to sell to librarians, who are a huge buying force, and if the librarians like your book, they recommend it to their patrons. There are a lot of untapped markets out there--i.e., readers--if you know where to look for them, and publishers know where to look for them.