I don't know that it's even that complicated, CK. The frankness about sex is really just a product of math. To wit: if you are straight, your chances of finding a viable partner without making any special efforts are pretty good. If you are a lesbian, those chances are much worse. So it's only natural that when you find more lesbians you're likely to form a community, and because your community has one big factor in common, it should be no surprise that it comes up a lot. Dammit, what a waste of what could have been a fantastic dick joke.
Yep, it's 3am, I need to get back to studying, and I'm just mad I couldn't make the double entendre work.