Me thinks we get a skewed view of things since, hey, this is general discussion. I think the general majority of the community doenst even touch the lower forums much, if at all. The most active areas of the forum are DF general discussion, other games, forum games and general discussion, me thinks.
And since the general outlook one gets of the general discussion populace is that of a welcoming community that seems supportive of people in general regardless of gender identity and sexual preference, it becomes a place in which non hetero and non cisgender people become more visible. This doesnt necessarily mean the community at large is made up of those people, just that they're far more visible in here, since it gives them a nice place to discuss precisely those things.
That said, there are other online communities that match DF's in regards to its openess to these kind of people. I'd say that our main advantage over these other communities is that we have Toady, who's not only a communicative and hardworking dev, but also a might admin who doesnt take it easy with people that step out of line. Not only that, he's pretty much the only person who has power to do that, so we don't get the usual mod power hijinks other forums get when they start giving some users mod status.
We also have a very diverse community in general, thus we can't really become an echo chamber, as even the most popular opinions get questioned and discussed, and no majority can go full toxic on the minority since they'll face the infinite wrath of the toadhammer, which is kind of what happens in communities that have a lot of people that hold one particular view very strongly (IE stormfront, tumblr tier queer communities, etc). Again, Toady is key to maintaining this kind of space.
Also, its because I'm here. I'm so gloriously attractive that I exert a gravitational pull on all kinds of people.