Thank you for the in depth reply! You make a very good point, and the timing of Apollo 13 with the budget decision is pretty damning, I'm convinced.

I will point out however that the budget was congressionally-mandated, and no funds were allocated for moon landings as they were in previous years; it would have been illegal to use funds dedicated to other areas for moon landings. Maybe I'm being overly pedantic here, but to say the 'funding was secured' as in the article implies the decision to cancel the remaining programs lay with NASA leadership; it would be more accurate to say that funding for the remaining programs, though possible, was not secured, most likely as an attempt to save face by congress/govt.