I don't think it's a coincidence at all. The way I understand it is that under Mormon doctrine, the act, not the temptation towards the act, is what's a sin: so a gay character who marries a woman and (regardless of whether he actually has sex with her or not) refrains from extramarital sexual activity is just fine and dandy. The Songbird character didn't get married; the Memory of Earth one did. But the former, while not "demonized", was presented as a fairly weak person; the latter was supposed to be a generally decent guy.