Wow, what an awesome (and rarely asked) question!
There are several types of Story Hours:
1. Game Journal - This type is made by a player of an actual table top (or PbP) game who is chronicling their character's adventures from the perspective of the character.
2. Game Account - This type can be from a player's or a DM's hand, but it is usually from a more omniscient point of view. It recounts an actual game being played.
3. Fictional Story - This is the product of an ENWorlder's mind. Someone above said that they are rare, and they are. Although, there are a coupld of well liked ones going by some pretty good authors.
There is no set rule to what Story Hour contributions have to follow. It's a place to tell a story. Some people like to read decent free fiction, so they go there looking for the fiction tag. Some people can't get enough superhero tales (since there isn't a ton of superhero fiction out there) so they get what they can out of the Story Hour forum. Most often, people visit the Story Hour Forum looking for a game like the one they are playing and mine it for ideas. That would be the most productive use of the forum - although there is nothing wrong with kicking back and enjoying a great read!
If you're looking for fiction, I will say that I am one of the "rare" - as stated earlier in the thread - fiction writers. You can see the link in my sig. One Story Hour {Bitterness Overcome} is a complete Story of ~180,000 words. The second Story Hour {Into the Moral Darkness} is a little more than 3/4 finished and it should reach its conclusion sometime in September. If you are looking for fiction, feel free to give them a read, and maybe even a comment or two!