A great many things the government does follow a similar over-promising, under-delivering pattern. The notion that perception is reality and a loss of confidence is the worst thing that can ever happen conspire to stifle public questioning.
We see it with Afghanistan, stimulus spending, TARP. As justifications don't pan out, something else is used to justify things.
Of course, the real root cause is that those paying for things are far removed from the decision making process. If voters individually decided whether they were going to be taxed $500 a year for continuing the shuttle or $100 a year for returning to disposable rockets, this program would have been killed long ago.
But everything is put in one big pot and dollars borrowed to conceal the actual ultimate pain. There are so many deceptive aspects to how this operates, its difficult to describe or even grasp.