Michigan is a swing state that always seems to go D at the last minute, kind of like Lucy pulling the football away from Charlie Brown. I could see it going for a Republican in 2016 with the right candidate (like Christie or Huntsman.)
Ya a "swing state" that votes for the other side by 10 points and hasn't been won by the other side in 1992 it sure is right up there along with the likes of Ohio and Florida.
That's only in strong Dem years nationally. In 2000, Gore only carried it by 5 points, and in 2004, Kerry only took it by 3 points. It's certainly not out of reach for the GOP by any means, at least in a strong Republican year.
May I also point you to Mike Cox, Terri Lynn Land, Rick Snyder, Bill Schuette, and Ruth Johnson, all Republicans who have won statewide races here over the past 10-15 years.