I think I'm with Nico on this one, because I do pass or have used un-official fire rings, especially back in "the day". There really is a need for them in well-trafficked areas and where, frankly, folks are gonna do a campfire somewhere.
As the elevations increase, I find them confusing and frustrating, however. Particularly in the Ansel Adams, where we come across fire rings in horse camps that are clearly used, well-built out and definitely "beyond" the no-fires lines on the maps handed out by the Ranger Station when you pick up your permit. So, I've asked the obvious question: "do the packers have permission to use fire pits because of their permits?" I get a "No", but the rangers aren't tearing out the fire rings/pits and there's no chance in heck they don't know they're there. What gives?
What's certain is that my compatriots on trail see them (I'm not above using the nice, flat, sides of rock rings to perch stoves upon), see the fresh charcoal and then ask about it. It's frustrating to have some things lean toward, "well, others may be doing it, but we're not", again and again.
In case this comes up, why use a drovers' camp site? Well, if you've got a large group, it's way more LNT to use the established site and spread around that. Just gotta dodge the apple zones when placing tents about the area. :) Of course, the larger the group, the more incentive/desire there can be to sit around a campfire...