FWIW: This same phenomenon is part of the same reason the Democrats are growing in metro Columbus. Having a (perceived) moderate business sympathetic black mayor like Mike Coleman, who's actually popular among white voters, helps avoid the black city/white suburb antagonism seen in other metro areas like Cleveland and Cinci.
I'm a fan of Coleman and thinks he has done a great job as mayor. I recall when I was living there back in 1998 that there's a certain racial element in the campaigns between Coleman and his white Republican opponent. Columbus is one of the few large cities that are actually growing, and a lot of this growth owes itself to the endless sprawl of suburban and exurban communities built on annexed areas. The remarkable Democrat swing in Franklin County (20% from 2000 to 2008) is more a result of increasing diversity, greater education, existence of institutions like Ohio State Univ, Ohio State Government and growth of professional backoffice finance and IT jobs.