In 2012, an average of 2.01 personal fouls were called per game. Thus far in 2013, the average is 1.49.
Marty has kept data on personal fouls called, whether they were accepted, declined or offset, since the 2005 season. From 2005-2012, the average number of personal fouls called was 1.74. That means the 2013 figure is a decline of 1.49 over the eight-season average. (Complete data on cfbstats.com.)
The only season that comes close to what is happening this year is 2006, when 1.53 personal fouls were called. But that was also the season when the new clock rules were implemented, leading in a decrease in the number of plays per game.
So what's the reason behind the decline in personal fouls? Perhaps it's the new targeting rules.