Part of the reason the ACC did not go with a north-south type divisions is due to stronger emphasis, in general, on football for those schools in the deep southern region of the ACC. However, there is also another major reason: The State of North Carolina which is in the middle of the ACC, has 4 schools in the conference which are close together, and for the most part, have a preference to play each other.
In the ACC divisions adapted, each North Carolina school has a permanent member in its division, plus a North Carolina team as a permanent opponent in the other division. So, of the four, each is playing at least two others in the State for fb. True, something similar could be developed with a north-south division.
Another reason for the ACC's divsional format, is to maximize integration, since there are three new members. At the same time, the ACC tried to balance travel, knowing that the "centrally" located schools had a real advantage in travel costs. The geographic extremes, BC and Miami, were not placed in the same division, and the conference tried to employ some fairness in terms of respecting distance between and among members as well as accommodating each school's most intense rival in scheduling. As far as the Miami-FSU situation, other schools will have to step up to the plate in due time.
When the SEC added Arkansas and South Carolina and created two divisions, they tried, and successfully, to enhance the bonding of the geographic extremes of the conference. While the east-west divisions are fairly distinct, the permanent football opponents in the other division sought to help address the factor. Therefore, South Carolina in the east, plays regularly, Arkansas in the west (maybe the two newest members did have less of a say at the time). The SEC had revised from two to one, permanent opponents for each school between divisions. The inter-divisional permanent opponents in the SEC are: So. Carolina - Arkansas, Georgia -Auburn, Tennessee - Alabama, Kentucky - Mississippi State, Vanderbilt - Mississippi, and Florida - LSU.
With the ACC's geographic make-up, it should not be assumed that the models that work for the Big 12 or the SEC, would function best for the ACC.
Let's see if the ACC does indeed revise its divisions in a couple of years. For now, their model seems to be appropriate considering the factors of geographic balance, team strengths, and political variables. While the ACC made some unusual decisions during the past year or so, their divisional scheme looks as if considerable and compromising thought was involved.