I think you hit on why we rarely schedule Big Ten teams. Normally scheduling non-conference games is about balance. You want to schedule win-able games and more challenging games. This looks better from a credibility standpoint as well as from a fans perspective. It is more fun to watch a competitive game... unless you are in the Big Ten.
I also think it comes down to the fact that BYU can draw nationally. For example, I live in Miami, but I am already planning on making the 7 hour drive up to Tallahassee for the BYU/FSU game. I can assure you that BYU fans from throughout the South will travel to that game (it is probably cheaper than trying to get the mtn). More people at games = more money, plain and simple. Because of that and because of the scheduling component, that is why these schools schedule BYU.