There are just 26 unbeatens (27 if you count newly FBS Texas at San Antonio) left after 4 weeks of play so somebody had to be left out. Sorry Minnesota. Outside of the top 10 or so, I'm not too confident any of these teams will stick around much longer. But at this point you can't argue with zero losses.
Last week it looked like Alabama and everyone else. But Oregon and Florida State both had nice wins and are starting to look more and more like contenders. Kansas State and Notre Dame have also impressed.
Northwestern is the only team I have ranked that is left on Iowa's schedule. If Iowa was good this year, that would be a good ting. But alas, even all the unranked teams are going to be hard.