I agree with the poster who pointed out that you completely overlook how limited the roll of the Bs and Ts in LGBT can be. Lesbians have it easy compared to us bisexuals, though where I live, I really wouldn't say the lesbians have been absorbed into straight culture at all. Actually, there are many different groups of lesbians in the city I live, with something for just about everyone to be found. There is a group of lesbians who play sports (mostly various gay intramural leagues), lesbian who are more the butch biker type you reference, ones that like organic vegetarian foods and various crafts, hipster lesbians, a group who are really into the burlesque/drag scene, another group that are more femme and like cocktails and dinner parties with the gay boys, a group of non-athletic tomboy types who hang out at hole in the wall bars and house parties, and a group of serious activists (who tend to hang with the gay boy activists fairly often). I don't know that there's a cohesive lesbian culture, because lesbians are as diverse as straight people, but lesbians definitely aren't blending into straight culture where I live either.