I think it's a good hedge for NASA to have this policy, they probably selected a good pick in the first place, and if it went wrong they could probably easily replace the position [source needed].
Its similar to Monarchy vs Democracy. A great monarch can get a lot more done than a leader in a democracy. They can also do a lot more harm.
If you want to maximize the potential of a company, you must choose a great CEO and give them near-unlimited power. The problem is that most boards aren't qualified/able to find one, which is why founders that survive the filter to growing into a mega-company are the ones you listed- they are the ones who've already got one.
Tim Cook is doing fine, but he doesn't wield near the influence Jobs did- look how long it took him to finesse Joni Ive out of the company, despite his choices causing massive problems for Apple.
So you'd better do it outside of your regular job, adding up to a 120% workload.