One thing I picked up from that is the spread between NCAA defenses.
For example, there's only a handful of elite defenses. Look at Iowa and Illinois lines. By shaving 30 YPG off Illinois, they improve 29 spots. Do the same to Iowa, and they improve only 3 spots. It's much more crowded in the middle of the pack. The difference between being top 5 in anything in the NCAA (like, I don't know, say Michigan in the top 5 in offensive yardage) is a huge advantage.
By the way, I would expect the opposite end of the spectrum to also hold true (cough Michigan defense). I would be interested to see how much opposing offenses have improved by virtue of having played us.
Very interesting, worthwhile analysis.