In social and cultural terms there are a lot of differences between gay and lesbian people. They are also different from bi people. Trans people are in a different category because so many of us have more than one of those letters. We are T&L or T&G or T&Bi or T & Straight.
We have many more things in common than we have differences, however. A very large part of the trans community is lesbian, gay or bi. Large numbers of gay lesbian and bisexual identified people also violate gender norms and stereotypes. Cissexual butch lesbians and femme gay men all get discriminated against for the same reasons that transgender, transsexual and intersex people are discriminated against. The similarities between the various sections of the community outweigh and outnumber the differences. The lines of demarcation are so blurred as to be irrelevant.
Lesbians had to fight for inclusion back in the '70's. Bisexual people had to fight for inclusion after that and trans people are still fighting for inclusion. That said, these divisions only have meaning within our community and the educated portion of the general public. For all too many people, trans men and women are just very very very gay and because of that, as Jenny Boylan once said, we are all together in this fight because "we get beat up by the same people."
In other words, while there are cultural and social differences, we also have a lot of commonalities and, for sure, politically we are all in the same boat. Focus on the Family and their ilk could care less about the internal divisions within our community unless it's to use them against us (witness the effort against ENDA that concentrated on trans people and ignore GLB people). Most people don't even know about them, or care to fo that matter.
The reasons behind our political oppression are all too similar as to justify emphasizing the differences between the various groups within our community. We need also to acknowledge the fact that self-limiting attitudes play right into the hands of our political opponents who love nothing more than to see fractures in a political front that needs to be unified against their hateful animosity. There's a T in LGBT because the reality is that you can't honestly separate them.