When I ran my Dungeons & Dragons/World of Greyhawk campaign, I constantly spawned new subplots, new NPCs, and new locations. It was intentional; my goal was to throw a wide net of possible plotlines, and let the players choose which ones to follow. By campaign's end we probably had hundreds of unresolved storylines, but it wasn't a problem because the important storylines – the defeat of the giants in the Grand Duchy of Geoff, the defeat of the orcish overlord Turrosh Mak, the liberation of Obsidian Bay – did reach their climatic ends.
Star Wars is different. As the Game Master Section in Saga Edition points out, Star Wars is about self-contained story arcs that constantly refer back to themselves. While based on episodic serials, the Star Wars trilogies (especially the original) are remarkably self-contained. Take Lando Calrission. We meet him in The Empire Strikes Back as a charming swindler turned respectable administrator … and the previous owner of the Millennium Falcon. In Return of the Jedi, when it comes time to find someone to fly the Falcon into the Death Star, Lucas turns once again to Lando rather than introducing some new minor NPC.
As a fan, it feels strange to see someone else flying the Falcon, but we feel better about it because it's Lando. It used to be his ship, and we believe him when he says she won't even get a scratch.
More importantly, stories actually end. My Shadows of the Force campaign for Star Wars: Saga Edition has seen several major storylines reach conclusion: the initial fight with the pirates of Zebulon Prime, the battle with a Dark Side cult on the backwater world of Maltern's Folly, the final showdown with the of the pirate fleet of Ral Duris, the penultimate confrontation with a Sith knowledge cult.
Of course, we've concluded storylines before – that's nothing new. But since we've started with Star Wars our storylines have been tighter, more focused, and more likely to conclude in less than 3 years. Each week when I sat down to work on my adventure, I had to force myself to think "How can I tie this into what's come before? Will this new subplot needlessly complicate things?"
It's not about railroading players down a certain path – the group still has a lot of leeway in what they do and how they do it, and if they want to go charging off in some new direction, they can do that. That said, as a group we've been working towards these tighter storylines; in our forums we have a list of outstanding plotlines. It's there as much to guide their decision as it is to guide mine, and it helps keep us focused.
Which isn't to say that I don't slip up. During the conclusion to the "Spires of Xax" storyline, our heroes' mentor – the Jedi Knight Lornn Varri – got into a lightsaber duel with the Sith Dark Lady Aldera. She fled through a portal in space/time created by the Spires, and Varri followed. Now they're both hanging out there in limbo; I wasn't ready to conclude that particular part of the story, and we were about to launch into another arc.
Is it good or bad? Well, it's bad in that I had a chance to close out the major story arc and didn't, but it's good in that there's this very Star Wars-esque/serial style cliffhanger still out there. And some day I'll figure out how to resolve it…
Not every storyline has to be concluded. The DeadStar storyline features a nefarious Rodian businessman named Geelo seeking revenge against our heroes for jumping a salvage claim. He's manipulated the judicial system on Taris to get a legal judgment against them and a bounty placed on their heads. It's a recurring storyline that the PCs can choose to end at any time … if they're confident they can actually win.
The counter argument can be made that Star Wars isn't about tightly woven, self-referential stories – one look at the Expanded Universe will show how even the most minor character, like a certain Rodian alien in the Mos Esiely cantina, can spawn entire story arcs. But I think this isn't because of the story telling – it's about of the fans. One of Star Wars' biggest attractions is its lived-in feel. It's achieved by packing each set and encounter with a host of interesting looking aliens, technology and structure, and you can't help but want to go back and learn more about that weird creature with the hammerhead like skull.
While the novels have tended to spawn ever more expansive storylines to take advantage of this depth, the most successful ones (e.g. Timothy Zahn's Dark Force Rising, the Knights of the Old Republic comic books) keep things focused on the main story. It's a tactic that translates well to role-playing games, and it fits our current style of play perfectly. That's because unlike 10 years ago, when I could count on everyone being that the game every week, nowadays with wives, kid and ever-busier jobs, it's impressive if we have the same set of player characters two weeks running.
The old "thousand plots" approach wouldn't work for us now, but the Star Wars episodic serials do. While players may miss one or two parts of an arc, they're usually there for a good chunk of it, and the obligatory Star Wars crawl helps get everyone on the same page.