Jeez, I wish I'd been here earlier. I could've saved Serebii a lot of trouble and this thread a lot of pages.
To restate was has been said too many times:
The Prima Roster is FAKE!
How do I know this? Because the original poster denied it in the very same thread the fake roster was posted in. Again, this has been said many times.
http://i14.photobucket.com/albums/a340/Dark_Random/fakeleak.jpg
There is the original post. Many of you seem to be under the impression that the Nintendrone was the first to "leak" it. This is not true, that blog took it from this thread.
I followed this thread to it's conclusion, as I too, thought it looked authentic (there was most likely some Isaac bias there). After suckering in a lot of people into the thread, the user posted an "image of the back cover of the Brawl boxart". This was just a delibrately bad Paint job, and after that the user confessed to being fake.
However, the damage was already done. Other users took it to other forums. The Nintendrone posted it up, spreading the roster further, and not everyone caught the admission on Page 16 or whatever. MetalIceWolf (The user who had created the "Roxas XIII" account for the purposes of "leaking" this roster) made another thread with the intent of announcing the fakery, but still this did not stop the spread.
Taking a detour here, as you can see, this was posted on the 4th of December (for me, though I'm Australian, so that would make it December 3rd in America). So it's no great big surprise that the characters up until there are in order. The Sheik and Olimar thing, however, is just one big coincidence. People do get lucky with their guesses, you know?
Since I know no-one here will take these words without proof, I've hunted down a non-GameFAQs spot where MetalIceWolf admitted making it up.
http://www.thewiieffect.com/2007/12/06/brawl-roster-leak/
That site ran the story. On the 3rd comment, she admits making it up. She has her own picture of the first post from after the mods took it down that proves she is the original poster (You can only view your own moderated messages).
I hope this clears up any final misconceptions about this roster.