An undefeated record used to be the ultimate measuring stick in college football. Back when polls determined national champions and bowl selection wasn't as structured as it was now, seeing that zero in the final loss column meant a team was title material.
Things have changed in a big way for the game over the last several decades. In the 1990s, the Bowl Coalition and the Bowl Alliance led to the BCS, all of which tried to put the two best teams in a national championship game. More one-loss teams got shots at the title. In the 2007 season, two-loss LSU won it all.