[NIX]

I agree with the rivalries argument. Conferences and divisions give a good reason to have an unbalanced schedule. And the more often you play the same teams, the more likely some bad blood will develop with the players being able to do something about it since they'll see that other team again shortly rather than letting it die down if you won't see Team X again for another couple of months or years.

Also, baseball has the obvious reason of the different leagues using different rules.