I think this is another one of these myths that needs busted.
The past two years this appears like an obvious observation with OSU and Michigan going undefeated both years (a combined 26-0 so far), but this is not the 60's and 70's anymore. Northwestern has won three championships in the past 10 years. Wisconsin has won a few. Illinois just won it five years ago.
I guess I'm of the opinion that if you struggle or lose with the "mediocre" teams in your conference you aren't a truly great team. You better hope other teams out there struggle as well. Take UK, they have done nothing this year, but beat LSU. They are the equivalent of a Purdue. Now, had Purdue beaten OSU they would be the media darling. They would be 8-2 and I guarantee a top 15 team. But they lost, so they don't sniff the top 25. And the Big Ten must be weak because they LOST. Now go back to UK, a team that you probably could compare to Purdue. They beat LSU and now not only is UK this great program all of a sudden, but LSU must be great too, because the SEC is so super deep that a mediocre program could beat one of their monsters.
If Purdue beat OSU, it would have been "proof" that the Big Ten was a joke.
Double standard and another circular argument it seems.