But I do think that to ascribe their getting together to the friendship rather than their "straight" desires and feelings of connectedness to the one other person who understands may come more from external logic and slash tropes than the actual text...

Okay, I think I'm starting to see where we've all been miscommunicating. Because as far as I can see, no one's suggested they come together because of their friendship - we're saying that the friendship is what makes the other even possible. Or are you seriously suggesting that if it weren't John and Rodney but, say, Rodney and Kavanagh they'd end up having sex with each other too, because after all they share the same experience?