You would be very likely to have ties between #2 and #3 where those two teams didn't meet.

You're also going to be putting a much greater weight on the scheduling luck of the draw.

With divisions, even if you're stuck playing a really good team from the other division (e.g. how we had to play Matty Ice in 07), if you run the table in your own division, you're pretty much assured of making it to the ACCCG - that loss doesn't kill you. But now, you could lose out to a team that had to play neither you nor Matty Ice and went undefeated, despite not playing the two best teams in the conference. That just doesn't happen with divisions.

We'll see it in basketball - in years when Duke and UNC are blowing everyone out, someone might just play each of them once, and get one of those games at home, and have a huge advantage over someone who has to play Duke and UNC twice.