The way I see it is this: the title says "How does a polyamorous relationship between four people work?". Okay, so this article is going to tell us how a poly relationship works, right? They then go on to say:
If any of the four want to get involved with someone else, they have to run it by the others - all of whom have a veto.
It just seems as if it is this veto that protects the people involved. I'd have preferred if they explained that a veto is something they do, they need, as with the permission to date other people rule they have is. It isn't something that people need to have successful poly relationships. I just think to the layman, it would appear that it is the veto that keeps this running smoothly.