Amen Michelle, amen.
I've heard of many stories and believe it or not; many pull it off. For every one who is outed 5 get away with it.
Also allot of it has to do with how you sell yourself or what sort of transition you went through. I hate to oversimplify; but it's the same old attractiveness level problem that all women have. The attractive have nightmares trying to shift through masses of insecure spineless twerps, where as the unattractive will have a nightmare just finding someone at all. The former is why I could not stand to leave my love in the dark about my past after a month or so, he seemed so un fazed and genuine and now I know he is.
The vast majority of what is sold as love is just infatuation... It hard to believe that even just 30% of the random people I meet have the limited humility and selflessness needed to really love someone. Plenty of people I know are outwardly polite and nice and giving, but even among there ranks I know allot are simply not relationship types.
True love is rarer than hens teeth to begin with, the vast majority of lasting relationships are just because they can tolerate each other. But when 'we' find someone who wants to stay with us after finding out, and then years later you know we have it

The long relationship pretenders would never do so for someone who has transition in the past. People change, but the signs are always there if you are astute.