i think tolerance is a better word to use. It is obviously best to keep animals as close to the conditions of the environment they are used to.
However, they will tolerate some other conditions.
Both adaptation and evolution are long term processes and would occur over a much greater time than we have been keeping herps...but they do acclimate to certain conditions (this is what I think you mean)
They probably acclimate to conditions that are reasonably similar to their native environment. When you say 60-65% humidity is "fine" for bloods, you are probably correct, becasue they can tolerate it because it is reasonably similar to their native environment.
I dont think theior care is changing, I do think, however, that the more generations produced in captivity the less "fragile and susceptable" the species is.
anyways, thats just my opinion
Im not even sure I said anything useful OR answered your question...sorry