Rematches can and do occur in the larger conferences that don't play round-robin. Of course, they happen much more infrequently than every year. I think that what gets lost when people get buzz-word happy and base the whole argument for a game on the magical "13th data point," is the reality that an additional data point can be either positive or negative.
There would over time be some years where the 13th would be BOTH positive and DISpositive (meaning the team winning the conference championship game would be excluded but for the win from the playoff).
The question remains though would those years be frequent enough to MORE THAN offset the years where the 13th is negative and dispositive and the only viable Big 12 team gets excluded because it lost the game. This year provides an example of that potential. OSU was second and lost to OU in the regular season finale. Had they played again the next week and OSU won, the Big 12 would almost certainly have had no team in the playoff. Rematches also don't become that hugely less likely if we went to 8 games. Rematches would not be the only possibility but when every team plays 8 of the 9 others they would remain very common. (Especially if UT gets it act together and annually plays OU.)
Moreover, the negative 13th point possibility is, of course, not limited to a rematch scenario. Let's say we did revert to 8 conference games and the championship game was not a rematch. It would still be damaging if a 11-1 team lost to a 10-2 or 9-3 team it had not played. Going to divisions would probably increase the likelihood of games where the team entering as the lower ranked team had no viable shot at the playoff even with a win. If the best 2 teams are in the same division you necessarily have at best the 3rd team in the championship game whereas without divisions the game would always be the "best" 2 teams playing.
Now, money, exposure, etc., might still tip the scale in favor if having a game but in terms of getting teams into the playoff, it could easily hurt as or more frequently than it helps.
The other thing to think about is how long will the playoff remain at only 4 teams? Once it goes to 8 then our champion would virtually (if not by rule) be assured a spot and having a championship game then that is won by the #1 team could knock the losing team out of the expanded playoff.
It's good we got the ability to decide how we want to proceed, but that doesn't mean we should rashly jump into a championship game.