pfc

Sure, some poly people view things that way, but many, many people don't. The problem here is that the comic is talking about the definition of poly, and equating it with triads.
Don't get me wrong, those relationships absolutely exist in the poly community, especially when everyone's queer. If you're dating someone, odds are good you'll be interested in the kind of people *they* are dating. I'm poly and I'm dating a partner (D) of my primary partner (B)'s partner (K), and D is interested in dating B-- and I could see myself dating K. So if that went down, we'd all be dating each other. At the same time, just because of the dynamics of our group, that would be a series of separate relationships, even though we hang out together a lot.
But also, including everyone's partners in your "family" can sometimes be downright impossible. When you're talking about a large community, it would be a logistical nightmare. Pretty much everyone I'm dating, or who is dating someone I'm dating, has a long-distance relationship with someone who has their own poly community where they live. Not only am I unlikely ever to meet these people, I'm definitely never going to meet their partners!
So I have no objection to acknowledging the existence of triads... I just think it's important to clarify that "poly" is a broad term for dating multiple people (not necessarily all at once) and that specific types of relationships within that (solo poly, triad, primary, anchor, etc) are just that, subsets. It's frustrating that people assume that because you're poly, you're a. in a sister-wives scenario or b. in a triad relationship!