Simple, yes, but is the policy particularily sane? Consider, for example, if I were to claim I was a duck. Should my wikipedia page pretend I have been a duck all my life? That would be preposterous, because as anyone can see, I am human.
Our science and medicine cannot change a person's sex, we can force the body to act a bit more like the opposite sex through constant medical intervention, but nothing more than that.
People's inner feelings fail the "soundnote is a duck" test: There are quite a few MtF writers, for example, whose style of communication is clearly male despite their self-identification: They physically are men, and have grown up as men, and their thinking clearly fits the male mold such that seeing a female name under their text just feels off. Just as I am not a duck, they are not the sex they wish to, even if they say so.