Before you spout off some stat you looked up on the internet you may want to think twice. If you actually attend the games, you will see that anywhere from 65% on a bad year to 75% on early sell-outs are BYU fans. It has been a home game essentially for years. Your point that BYU is not a big draw... lets see:

Sam Boyd capacity: 36,800

Attendance:
2003 25,000+ (no BYU)
2004 29,000+ (no BYU)
2005 40,000+ sellout
2006 44,000+ sellout (4,100 temporary seats)
2007 40,000+ sellout
2008 40,000+ sellout
2009 40,000+ sellout (weather left some purchased seats open)

These numbers are easy to come by...

Another comment: When BYU played UoA in Tucson (I was there) I remember reading that it was the first non-ASU sellout in Tucson in 10 years! I don't think USC has sold UoA stadium out in 20 years. If BYU plays in the west, we travel very well thanks!