Sure, scientists and such are clever and will try to figure out how to continue to expand the sciences, even without financial support systems of the past, but the demand in aeronautics will continue to diminish, fewer experts will get involved, and any incentives to stay will simply go away.
This budget restores funding to the science and technology development programs that Constellation cannibalized when it was under-funded. Aeronautics gets a 15% increase, for instance.
The truth is, there's no great plan, instead these cuts are politically motivated...
NASA's budget was increased, not cut.
Constellation was a huge unfunded mandate. It sucked all the funds from everything else NASA did. The Augustine report that studied future options for NASA said it would take 3 billion additional dollars per year to implement the program, and it gave several better options for NASA in the unlikely case that the $3 billion was available (but it isn't).
I see these changes as being common sense, not politically motivated. No politician of any party would want to borrow the money required to see Constellation through.