That's usually an artistic difference, rather than a technological one. Today's rendering engines are extremely good, but that's no guarantee the artist will use it in a photo-realistic manner. In fact, while CGI rendering engines have gotten better, moviemakers have trended towards a more stylized look even with live action—such as the dreaded "teal & orange" grading. Ironically, it is the CGI stuff that has realistic light and color, while live action is now filtered to death.
(Check out any of Andrew Price
I believe that. I often find myself yearning for some natural brightness and, heaven forbid, some primary colors in today's sci-fi movies.