The AP could have voted for Auburn just as easily in the BCS system than they could have in the old system. To say Auburn had no chance at winning a split le is pure speculation - assuming someone who voted for USC would have changed their vote to Auburn had the Trojans beaten Michigan instead of Oklahoma.
In the new system, the chances of a split le are reduced, because typically there are two clear cut teams competing for the national le, and they play for it. You want to abandon that to mitigate against the occasions where there are more than 2 teams deserving (which, while becoming more common is still rare). So now, instead of an Auburn getting screwed every now and then, there would be arguing over at least 1 team getting screwed every year.
Old System Bowl Games:
#1 USC Plays Michigan in the Rose Bowl
#2 Oklahoma probably would have played Georgia from the SEC in the Cotton Bowl
#3 Auburn would have played ACC Champ Virginia Tech (which they did anyway) in the Sugar Bowl
Assume all 3 win... how is that situation any better than USC playing Oklahoma and Auburn still playing VT, other than now there are 3 teams with a gripe instead of just 1?