Well of course ND has better odds to win the National Championship than OK, they're already in the top 4.

Bama's odds have increased over OSU because (1) OSU has Mich, Mich State and Iowa left; (2) Bama just made it through LSU and MSState; it has Charleston Southern, Auburn and Florida left. So Bama is more heavily favored in it's last three games than OSU.
Odds include odds of winning out. Big12 teams have most of their games in front of them too. Odds will change after the regular season is over and only playoff games are left; that's when it will be interesting to see what Vegas things about the actual matchups.