Urban Meyer won't be Ohio State's next coach. He will have made his name for himself long before then. Perhaps he has already "made it," at this point. Ohio State, in 15-20 years, will either promote from within Tressel's staff, or hire a successful coach from a smaller school.
I can't speak for everyone, but I can't see anyone wanting to be Tressel's heir to the Ohio State coaching job. You never want to be the guy who follows the legend. You want to be the guy who follows the guy who follows the legend. (Example: You'd want to be Urban Meyer more than you'd want to be Ron Zook.) (Exception: I'd rather be Earle Bruce than John Cooper.)