That's interesting. I'm surprised there's that large a statistical improvement on defense. As far as strength of opponents go, it seems to me that last year's first seven are comparable to this years, with two tough offensive tests in each year (USC and Missouri 2007; Missouri and TT 2008)
The Ball St. (610yds) and Oklahoma St. (551 yds) seem to be the games that really inflated those defensive numbers for 2007. As disappointed as I was in our defensive performance against VT this year (377 yds), a team that I don't think has a great offense, it was certainly an improvement over those Ball St. and Ok St. games from last year.
I think also that because we were so overmatched and the game got so out of hand against Missouri this year, the number of yards we allowed was suppressed. If our offense had competed in that game, Missouri could've made a run at 600+ yds. Same goes for the TT game if our offense hadn't dominated time of possession the way they did. If the offense had moved the ball quicker, it's easy to imagine TT racking up 500+ yds. We didn't really stop them all day.
In other words, I think we're a slightly better defensive team, especially against the teams that we should be able to contain, like VT this year, unlike Ball St. and Ok St. last year. I think that against good offensive teams, like Missouri and TT, we are vastly overmatched and incapable of containing. The good news is that the coaching staff, at least in the TT game, found a way to control the clock and give us a chance to win with a minimal contribution from our defense.