Average staring field position is at 28.4 yards:
http://www.footballoutsiders.com/stats/fpa

This does not differentiate between drives that start after kickoffs, punts, or turnovers, but it does exclude drives in garbage time.

This site below shows that BYU ranks 37th in opponents' average kickoff return yards:
http://www.cfbstats.com/2014/leader/national/team/defense/split01/category05/sort01.html

You can see that BYU is near the top in kicks returned, which makes sense because they have had very few touchbacks.

So what does this all tell us? Nothing really. I don't see any statistical advantage to avoiding touchbacks, but there's really no proof that it isn't. If Bronco is, in fact, avoiding touchbacks for better field position, he's probably the only coach in CFB doing it. Kicking to the 5 rather than in the endzone does give your cover team the chance to pin the opponent down further back, but it also risks the return guy taking it back all the way. The additional risk of injury should also be considered. In my opinion, it would be a mistake to avoid touchbacks. I hope Bronco isn't really coaching the team to do this.