This is not the same team that played in 2010 and we aren't playing the same opponents.
The dumbest argument for predicting who will beat who is the historical one. "team A has beaten team B in 3 of the last four match-ups on the road." "Team C can't win outdoors in November and December." "Team D always plays better on the road than they do at home." The past has little impact on the present and future.
The 49ers were 6-10 in 2010 and 13-3 last year, with Alex Smith, no less! The Lions went from 2-14 in '09 to 6-10 in '10 to 10-6 in '11. And it goes both ways. In the last 3 years the Vikings went 12-4, 6-10 and 3-13. The Colts went 14-2, 10-6 and 2-14. Those are just a couple of recent examples.
There is every reason to believe that the Chiefs will be a much improved team this year and only two reasons not to--pessimism and some people's opinion of Matt Cassel.