OSU is #1 because they are the defending champs. (LAST YEAR) (Every SEC team would argue that OSU would have multiple loses if they were in the SEC.)
Indiana has been ranked above SEC teams all year because last year they showed they were for real. (LAST YEAR)
ND has basically the same team back from an impressive playoff run and it has been reflected in their ranking this year. The highest ranked 2 lose team for most of the year. I would argue, because of how well they performed in the playoffs LAST YEAR.
I think LAST YEAR has played a big part if the IRISH rankings this year.