Only fucking idiots think that the NCAA overstepped their authority. They didn't overstep anything. I skimmed through the Division I rulebook (and have posted it several times in this thread) when Sandusky first was on the front page. There is (as I assumed there would be) an early ethics section that was clearly broken. Usually, when a member of a membership organization egregiously breaks the early ethics section of the governing rules, the normal response is simply to expel the member. Unless there are specific bylaws spelling out what to do in that specific situation, whatever board or committee governs the organization can do whatever it wants. Penn State agreed to these decisions because they knew that the NCAA had the leverage with its perfectly legal powers to expel an unethical member institution.
Unless there are specific rules outlining how to deal with covering up and enabling child rape, the NCAA Executive Committee had authority to do anything they wanted. If Penn State can't abide by their decisions, they are perfectly within their rights to refuse to comply and exit the NCAA.