No, I'm not talking about Fourth Edition -- I'm talking about two "traditions" of older gaming that seem to have fallen by the wayside over the years. They were both staples of my youth in the late 70s/early 80s and it's been years since I've seen either one in action anymore.
The Big Group: OD&D recommends a ration of 1 referee for every 20 players, although it notes that campaigns can reasonably handle up to 50 players without much difficulty. Now, I never played in a campaign with even 20 players, but I frequently played in adventures with a dozen or more players at one time. My regular gaming group consisted of 6-8 players on most occasions, sometimes more if friends were visiting. They'd bring their characters and, if the referee approved, they'd simply drop into the campaign and play with the regulars. Many gamers nowadays look with befuddlement on the notion of a party leader or "caller," but, back in the day, he played a very necessary role. When the adventuring party consists of 12 guys sitting around a table, a caller is the only way to get anything done without total chaos erupting.
Over the years, the average size of the party -- and presumably the campaign as well -- has declined quite precipitously. I'm not quite sure why that is. The average size seems to be about three or four. My current group consists of three people, although a few years ago it had swollen to eight, counting the referee. Before anyone makes the unlikely claim that there's been a philosophical shift in gaming toward more a more "intimate" feel (let alone that it's closer to the pulp fantasy ideal), I suspect the shift in group size has more to do with non-gaming social dynamics than anything else. The graying of the fan base has meant that it's harder to coordinate the schedules of many adults than it was to get a dozen kids together. Goodness knows I can barely get three people together to game; I can only imagine the nightmare of trying to coordinate a dozen adults with jobs and families. Mind you, I've also observed that children don't seem to be as freely available to play as they were in my youth. It's the middle of the summer now and there are no kids out playing the neighborhood and won't be until the late afternoon/early evening, because they're all off at day camp/daycare while their parents work. When I was a child, this was not the case and, during the summer vacation, children could be counted on to be constantly outside and available for play from about 9 AM till almost 9 PM -- lots of opportunities to play D&D.
No wonder everyone's looking to the wonders of computing to save the hobby.
The Rotating Referee: Because groups were so large, this led to a second commonly accepted practice: multiple referees for a single campaign. In days of yore, it was simply a fact of life that, on some days, one guy would run an adventure and, on other days, someone else would. Indeed, it was rare in my experience that a player didn't at least occasionally don the referee's hat and take over such responsibilities. Now, granted, most campaigns had a "primary" referee or a pair of them, but that doesn't change the fact that most players in a given campaign would try their hand at the referee's role every now and again.
This is a change that I think owes to a combination of factors, some of them purely accidental and some of them philosophical. The accidental factors mostly pertain to the shrinking of the average group size. If you have only three regular players, there's not as much scope for referee rotation. On the philosophical side, though, I think there's definitely been a slow morphing of the concept of the "referee." He's now viewed not just as a neutral arbiter cum occasional opponent. Rather he's now a "storyteller" or "narrator." He's the guy who creates the "story" of the campaign and keeps it moving in accordance with his grand plot. Given that, it's much less easy to accommodate a second or third referee, because they'll almost certainly spoil the story, or at least derail it, and that's not viewed as a good thing. In campaigns without explicit stories, a rotating referee just adds more details and events from which a story might later be woven, but there's no danger that he will "ruin" the campaign by introducing things that get in the way of some grand plan.
For myself, I miss both larger groups and rotating referees. They used to be givens and now they're, at best, rarities and, at worst, deemed eccentricities. I'm thinking about ways to change that in my own group.