Female friends tend to be much more touchy feely anyway. Although recent studies show that newer generations of both genders are becoming more and more sexualy open.
I can very easily see Devin Brugman and Natasha Oakley as lesbians or bisexual. They never seem to leave each other's side, and they even have matching tattoos on their wrists. That, and both women come across as very sexual and thus willing to kiss each other and experiment in other ways.
Rachele and Nikki are sexy in very different ways. Rachele is a rarity of having a super toned body, yet also having a pretty and feminine face. Most female celebrities never have the devotion to fitness that she has. Sure, they may lift a few weights to get into shape for action roles, but only Jessica Biel has gotten into tip-top shape and stayed that way for many years. Meanwhile, Nikki has the whole "I'm an adorable Asian girl" thing going for her; she's more cute than sexy. And if you watch her daily videos, she's always talking in this child-like voice. So they have sex appeal in their own ways, but they don't come across as overall sexual compared to Devin and Natasha.
But again, I'm pretty sure Rachele and Nikki are aware that their friendship can be mistaken as a lesbian relationship, like when they were teasing in another Q&A video that one of best things about do these Facebook sessions are that they have to cuddle with each other in order to fit into the video's frame. So they are aware of it, but haven't fully explored it.