Highest of respect for what these gents has accomplished during their career including Dr Armstrong's post-NASA professorship at an university.
But I think they've misplaced the target of their anger. It is Congress that sets the spending parameters and they have been reluctant to increase NASA funding in turbulent economic times. So NASA could only afford one major programme not two, unfortunately.
NASA had to make a choice between a rock and a hard place. Either way, no real winners.
I am sure Mr Obama would have signed a bill into law that specified increased funding for NASA to cover a short-term transitional gap between one programme to another.
Part of the problem, though, is that nobody has a clearly articulated 'next step' vision. The Augustine Committee was tasked to find the most feasible option that could be affordable and implemented. The news they gave was bleak; no realistic short-term option at present funding levels -- perhaps by 2030s.
Hope right now is that private industry may be able to step up to fill the gap. SpaceX seems promising and there are others on the horizon. That may be several years away, though.
Ultimately I think Dr Armstrong and Mr Cernan may want to lobby Congress for increased NASA funding or continue their present life rather than blasting the President and NASA.