I think we're overlooking a few key facts:
1) Illinois had two weeks to prepare for Nebraska. Two weeks to install sets that Nebraska wasn't able to see on film because there was no film on it. Two weeks to get healthier to go up against a Nebraska team who was playing its fifth game in a row. Plus, Illinois features a couple of running backs and defensive ends that were expected to give Nebraska's defense problems. That Nebraska held Illinois to 270 yards and 16 points while putting up 423 yards and 31 points is a good performance, a performance that should continue to build confidence.
2) Wisconsin's defense is great, very fundamentally sound and they've put up good numbers against Michigan State, Michigan, and LSU, all of whom have QBs who can a) run but not throw or throw but not run. However, they haven't faced a true dual-threat QB, and won't until they play the Buckeyes. I hope Langsdorf really pays attention to what Ohio State does against Wisconsin as that should give him the blueprint for what Nebraska needs to do to beat Wisconsin. I'm not convinced our offense stands no chance against their defense.
3) Michigan State really isn't the Michigan State of last year, and though Indiana's win is surprising, it wasn't completely unexpected. State's wins this year have come against Furman who was only a possession behind the Spartans heading into the 4th quarter and a Notre Dame team who has already fired their defensive coordinator. State has struggled offensively, yet was able to rack up over 400 yards of offense against the Hoosiers. State's secondary struggles, yet they held Indiana to fewer than 300 yards through the air. The Hoosiers are without doubt an improved team this year, but Nebraska should handle them.
Needless to say, Nebraska's season is going to come down to how they perform against Wisconsin and Ohio State. They've shown they have the talent and will to win at least one of those games, and nothing I've seen tells me they won't.