Yeah, my guess is that this an an artifact of cultures which are more traditional in that intergenerational friendships are more common.

Eg, in England, you friend your friends on facebook, then begrudgingly accept your mom's facebook request.

I Mexico, you accept friend requests from your mom's friend, Gloria, your dad's coworker Edgardo, and of course, your entire extended family tree. In these more religiously/sexually conservative countries, the actual people people spend their time with and relate to are probably more gender-matched than in more secular, liberal nations. But this effect is washed out by the sheer number of loose connections that any given person has.