First USC's offense didn't put 30 on us...they put up 28 (one of their five TDs was an INT return).
Second, that was at USC where the crowd was about 95% USC (I know...I was there), and not at a neutral venue where 60% or more will be Buckeye fans.
Third, our offense was in disarray at the time (splitting QB time between Boeckman and Pryor, Beanie Wells out hurt, at least one key OL was out IIRC). This put an additional burden on our defense as they were on the field more than usual.
Fourth, our DL was vulnerable to the run. Since then, our DL has made significant improvement in run defense and in generating a pass rush. It is a markedly better DL than it was three months ago.
For Texas to beat us by 20+, they'd better score 45+ because we're going to score as a minumum of 24 points...and there's no way in hell Texas is going to score 45+ points.