Nothing wrong with it, but I have noticed this trend myself. Who knows why that's the case, but I think it's not too different than the general population. There are a lot of straight people who are more open then they claim as it is hard to find the appropriate label. For example, I consider myself to be straight as I only want to date men, but I do acknowledge that are girls out there that I think are attractive. It just stops there for me because I really don't want to date or be intimate with another girl romantically or physically. Maybe bicurious is a better term? Still, I find straight to be the most appropriate label for me because of my romantic and physical inclinations. See, labels are tricky and I know plenty of straight women and men who are just like me in this regard. And given the fact that transgender people are more open to the lgbt community and more likely to be educated on lgbt issues, we may be more vocal about our preferences than the general public.
Having said all that, my exposure to the trans community (here and in other avenues) has been that most lean somewhere in the middle rather than on either extreme. I wouldn't assume any statistical significance on this as it is just my experience, but the majority I have run into are bi, then I'd say gay and then straight. Just what I have seen.