Here is a good article reasoning why:
Factoring in stuff like.. no rookie QB has won a SB (sayonara Indy, Seattle, Washington and Miami), no team in the history of the SB has won it after losing by 28 or more points in December (bye Texans and Giants), and only twice has a team come back to win a SB after losing it the previous year (seeya NE).
If you eliminate the above, you have left: Denver, Atlanta, Green Bay and Baltimore. Longshots are Dallas, Pitts and Chicago.
And they are betting it will be Denver (4-1) and Green Bay (6-1) in the SB this year.