I think that the logic behind fake/realy jewerly is this.
If the gift is a token of appreciation then the content of the gift is not so important (I am not dismissing the fact that the nicer the gift, the bigger the token)
However if the gift is for an engagement or for a relationship, then the gift has to be real, since it is the content that matters.
I know people that order fake jewerly similiar to their real ones, so they can leave the real ones in the safe, and carry the replicated ones..