While it is not surprising that the ignorance defence is the way these CEO's are going and that large and diverse companies may be difficult to keep tight control of, it is also difficult to let them off the hook with this sort of defence.
The CEO is responsible to ensure that he/she puts into place the systems, procedures, assessments and controls that ensure companies run correctly.
In addition, and at least as important, it is the responsibility from the top to implement the correct ethical style with no cutting of corners.
This also means that rewards, incentives and promotions should be linked to doing the right things and NOT just results, regardless!
Being at the top is tough and the responsibility is heavy and not for everyone!
Related links:
Ebbers: Giant Fraud, Simple Conclusion