Things are actually just a little more complex than you may realize. This is because it is NOT the case that all "romantic relationships" or even "passionate bonded relationships" have a sexual component, per se.
While it is less common, and less commonly understood, today in America and in the world/west...-- as contrasted with, say, the 19th century --, there is a tradition of "romantic friendship" http://en.wikipedia.org/wiki/Romantic_friendship
. This tradition makes me wonder whether it is at all proper to call people "lovers" simply because they have a sexual relationship. After all, many sexual relationships aren't all that damn loving.
So sex, again, isn't the most central or core thing in polyamory. Love is. Whether a group is a V or a triangle, I suppose, depends more on the quality of love than the quantity of sex between the participants.