As I mentioned in my post, anyone (including primary couples, even legally married ones) are certainly free to determine how "out" they want to be.
That said, nonprimary partners should be similarly free to decide how out, or how closeted, we're willing to be about our own relationships.
The trouble is, often people in poly primary couples don't disclose clearly to their additional partners the kind of closeting the expect their partners to go along with. Too often its something that only becomes evident well after a nonprimary relationship has been established. Frankly, that's really unfair to, and inconsiderate of, nonprimary partners. We deserve enough clear information, early enough in a relationship, to be able to make informed choices about how involved we want to get -- if at all.