The upgrade from 8.0 to 8.1 is pretty specially tailored/designed by Microsoft to run with minimum interaction with the user and to take over settings, installed applicatiions and data files transparently so it would not surprise me if it ignored and need for administrative passwords. Assuming that if you were corrdctly logged into the 8.0 you would be who you are supposed to be.
I was certainly no asked for one ..... but don't have anything other than whatever is the default.
FWIW ...