Not so much anymore.
While it is still a touchy subject (see the footnote to the attached article), museum directors and conservators are beginning to let things fluctuate a little in the name of saving the environment. It takes a tremendous amount of energy to maintain precise humidity levels and studies have consistently shown that gradual changes in humidity do not damage artifacts.
No less a director than Sir Nicholas Serota, director of London's Tate galleries is chiming in:
Standards under attack!"We need to devise imaginative new solutions to resolve the dichotomy between long-term collections care and expensive environmental conditions,"Read more in the Guardian.