For obvious reasons, the people who are most able to find a good gig elsewhere are the most likely to elect to go do so; and they tend to be the people that you'll miss more.
Im not sure this applies. Good people at NASA were already capable of easily finding higher pay in the private sector.
People work at NASA because they believe in the mission. So if they are leaving now they either stopped believing in the future of NASA because of this or they were money motivated and sucked.