I assume part of the reason for the optimism is Iowa's OL tradition specifically it's OL coaching. The thinking being that Iowa's coaching will work out any bugs with a couple of "new" starters. Ed Cunningham, the ESPN announcer who did the OL ranking, is a former Washington center and played for 5 years in the NFL so he should have some expertise in OL evaluation. A little surprised Iowa's DB's didn't warrant a top 5 ranking w/3 of four starters returning from a strong unit.
http://espn.go.com/college-football...es-rank-college-football-best-position-groups
http://espn.go.com/college-football...es-rank-college-football-best-position-groups
http://espn.go.com/college-football...es-rank-college-football-best-position-groups
http://espn.go.com/college-football...es-rank-college-football-best-position-groups