Technically, that way you think of gay men typical talking is not called an accent, but a sociolect, which is a type of dialect. African American vernacular English is another example of a sociolect.
Whenever a community forms and wants to separate itself from the greater community at large, these sociolects tend to naturally arise. I am not personally familiar with the lesbian community, but armed with a little knowledge of sociolinguists, I would wager that there actually is a lesbian sociolect (as Lefted posited), but that it just has not been picked up by the media yet, and converted into a stereotype.
This has nothing to do with being “masculine” or “feminine”—- straight, gay, male, female, everyone communicates!!