One of the more interesting aspects of the early days of role-playing games was the assumption that campaigns were something that lasted some time. Certainly Greyhawk and Blackmoor lasted a very long time - but in the first decade of gaming, there did not seem to be any sort of assumption that a campaign would end. Reading articles from early issues of The Dragon, it's quite clear that campaigns did not die (but they might fade away).
I know this era of long-lasting campaigns didn't last. In fact, one good reason for them not lasting for regular play was simply the appearance of new role-playing games. If you wanted to play a different game, and your group met once a week, well, something would have to give. "D&D or Bushido? It's your call!" "How about Boot Hill?"
Now, it seems that campaigns are envisioned as something to start and then end. Case in point: a friend of mine ran a 3rd Edition D&D game set in the Forgotten Realms, and while I enjoyed it, I found that he had plotted a specific "story arc" to end at a particular point in the campaign, and then it was done. I had mentally prepared my Tiefling paladin (not angsty, just different) for a longer period of play, so the end of the adventure was something of an abrupt stop for me.
But in the present Old School Renaissance, we've got the chance to figure some of this out in advance. I think there is something qualitatively different to an open-ended campaign, in comparison with those with pre-set ending points. I'm not saying that a campaign must be played constantly and forever, but more a difference in viewpoint about beginnings and endings. Put somewhat more philosophically, I think that the duration of a campaign is just as much a part of the "sandbox," so to speak, as the geography of a campaign.