"Set in 2013, 10 years after the Raccoon City incident" <- that doesn't sound right..?
It doesn't since the Raccoon City incident occurred in 1998. I decided to research the Resident Evil timeline, and got this.
July 1998 - Resident Evil 1/Resident Evil Zero
The Mansion Incident
August 1998
Chris Redfield learns of the G-Virus and heads to Europe to investigate Umbrella. By doing this he avoids being in the G-Virus outbreak that is about to occur on Raccoon City, and also helps setup Code Veronica when Claire goes to look for him.
September 1998 - Resident Evil 3 Pt.1 / Resident Evil 2
The Raccoon City Incident occurs
October 1998 - Resident Evil 3 Pt. 2
Raccoon City is destroyed with a missile strike
December 1998 - Resident Evil Code Veronica
Claire heads to Europe to find her brother
2004 - Resident Evil 4
The President's daughter is kidnapped and Leon is sent to find her
2005 - Resident Evil Revelations
Jill Valentine and her partner are sent to investigate Chris's last known whereabouts aboard a ship known as the Zenobia
2006 - Resident Evil 5: Lost in Nightmares DLC
This is when Jill and Chris learn of Wesker's whereabouts and go to confront him.
2009 - Resident Evil 5
Chris is sent to Africa to investigate the sale of bio-weapons in connection with a man named Ricardo Irving
So, according to the Resident Evil 6 synopsis if it has been 10 years since the Raccoon City incident that would put RE6's timeline in 2008 and not 2013. 2008 is exactly one year before Resident Evil 5. This could also explain why Chris does not have Jill at his side when she is clearly a major BSAA agent.
Here is something interesting I dug up that could still indicate this could be a prequel still
In the trailer we hear Chris's partner saying something about Chris's personal vendetta (http://www.youtube.com/watch?feature=player_detailpage&v=sS_bGpe9qE8#t=158s) not getting them anywhere.
Also notice how angry Chris was when he found out some of his squad mates were killed in the trailer?
This is taken from Chris's story file in Resident Evil 5, after the Lost in Nightmare DLC story:
After three months of searching with no success, Jill Valentine was officially declared dead by the BSAA.
No one knows what promises Chris made in front of Jill's empty grave, but following her loss, he redoubled his efforts to eradicate all bio-organic weapons wherever they may be. Initially stationed at BSAA's North American Branch, his investigations soon took him around the world. He became involved in so many operations that he soon had more missions to his name than any other BSAA member.
So following "Jill's death" he became more motivated and aggressive at eliminating all bio-organic weapons. Which would explain his aggression and personal vendetta that his partner in the RE6 trailer was talking about.
Then we have the part where "his investigations soon took him around the world" which would mean China in Resident Evil 6, and Africa in Resident Evil 5. Only China may have come first before Africa.
I hope Capcom didn't fuck up the timeline. It won't make or break the game, but it's something you would think they would get right since they got the timeline right on all their other games.