I think he feels misled on the scope of their problems though.
Word I've heard from an agent to an NFL coach is that O'Brien was told the Sandusky think would be a recruiting obstacle, but not an NCAA issue. He was misled considerably and feels that he could leave without having to pay as much of the buyout as is being reported (or any of the buyout at all), which is why he is gaining interest.
An NFL owner, while a billionaire, isn't going to pay $18M just for the right to hire a coach. He could add that $18M to the contract of someone like Dungy, Cowher, Gruden, etc. for that matter.