I would just point out that this a fairly recent interpretation of citizenship laws. In the laws in effect at the time Obama would have been adopted by Lolo Soetoro, there was nothing in the law that specifically prevented a minor from renouncing his own citizenship. It's also not clear what effect an outgoing adoption can have on a child's citizenship. One state department Web site acknowledged that the United States couldn't protect the citizenship rights of children adopted into non-Hague Resolution countries, such as Indonesia. What I think might be more overriding however is if Obama chose to exercise any of his Indonesian citizenship rights as an adult. It's pretty hard to claim NBC-status under such a scenario.
Yes that is different. Unfortunately even that might not be enough, had he been an NBC to begin with. The courts, and the laws, have made it increasingly difficult for citizenship to be removed involuntarily, and what counts as a "volutary renunciation" has also been narrowed.