Alves v. Fitch has always been planned as the co-main event for this event. They did not promote it that way at first as they were still making sure Alves was cleared to fight post-surgery. Once he was cleared and the bout was signed it immediately took its place as the co-main event as planned.
As for the quoted text: Because Alves is still the #3 welterweight behind GSP and Fitch, thus when #2 and #3 fight the winner deserves a shot at #1. It goes back to how I explained Rich Franklin getting his second fight against Anderson: Just because he was handled, doesn't mean he's not the #1 contender. It just means there is a dominant champion. Koscheck is #4 right now, Hardy wasn't a #1 contender, etc. Those were promotional match-ups to avoid having GSP vs. Fitch or Alves has they recently happened and GSP dominated. But now, with this fight it forces their hand in to making the winner fight GSP. With the addition of Shields one could argue that he deserves the shot, but this will be his first fight at 170 in some time, it's just unfortunate that he'll have to wait until after Fitch/Alves vs. GSP to get his shot (if he even manages to win both of his fights). The winner of Fitch vs. Alves deserves their shot and it's one totally based on merit.
dos Santos has very good BJJ, but it's not world class. Roy Nelson is a LEGIT grappler. dos Santos is without question the favorite heading in to this fight, but it shouldn't be that big of a gap to be quite honest. dos Santos has never been pushed, so we still don't know about his cardio. We could fight out against Roy.
All in all I look for Black House to have a very good night. Ed Soares has been in very good spirits and is a great guy to speak with, excellent guy. He'll be celebrating with his team tomorrow night after a Cigano title shot earned and Anderson's destruction of Chael Sonnen.