Continuity, or: How the development of modern story-arc-based TV parallels the development of webcomics
I was chatting with EC just now, and she was commenting that DVDs have really changed television by making shows with continuous story arcs more accessible.
I think this parallels the advantage of the webcomic. With traditional daily newspaper comics, you could not rely on anyone reading any particular strip, so you couldn't really sustain significant story arcs. Sometimes you'd have a few strips that all riff off the same story, and characters can develop a bit and change over long spans of time, but the comics generally had to stand on their own. This is similar to traditional TV shows, which had to be episodic, because you couldn't expect people to watch every episode, and you didn't want to alienate casual viewers.
With the webcomic, those barriers are removed in large part. If you miss a comic or two you can just click back to the archives and catch up. Even if you jump in to a comic a year or two late, you can start reading from the beginning of the archives. (I think this breaks down a bit once the comic lasts many years, when it becomes less feasible to catch up on all the backlogs, though, and in fact I see this as one of the weaknesses of the webcomic medium. But more on that later.) And so webcomics can have continuity whereas newspaper comics cannot.
A combination of Internet fan sites, DVDs, and episode downloads have done for TV what webcomics did for comics. Back in the mid-90s, Babylon 5 was an early experiment in a pre-planned story arc, and I think at least a small part of its success was due to the excellent fan-site Lurker's Guide that cataloged all the major plot developments from each episode. People never have to be confused by some major event (as long as they had Internet access, but Internet early adopters had at least a fair amount of overlap with Babylon 5 fans).
With the spread of cheap full-season DVDs, people could jump into a show in its second or third season by catching up on all the episodes they missed. This is what EC was talking about. And so shows like 24, Desperate Housewives, and Lost could have continuous storylines, and people wouldn't feel, well, lost.
I think the most recent advance is the downloadable episode (first illegal, and later legal). This allows you to catch up on a missed episode without waiting for a rerun, and even without waiting for DVDs to come out. Now you don't have to skip a beat before watching next week's episode. (I've been downloading shows from iTunes when I forget to tape them on my VCR, and so I'm annoyed that NBC is going Windows-only soon. :P But speaking of which, let's not underestimate the effect of Tivos, which made it easier to tape shows.)
Now, I'm not saying TV shows with story arcs are necessarily better than episodic TV shows. There are plenty of episodic TV shows that "reset" after every episode that are still great. Similarly, I'm not saying that webcomics are inherently better than newspaper comics, either. (Though I do think the newspaper comic world is a bit stagnant because of the limited space and the difficulty of canceling long-running comics.) Also, as EC pointed out, TV shows do still jump the shark, and that's of course true of webcomics as well. (Shark-jumping in shows with story arcs can be a bit more annoying, though, because you might feel more compelled to keep watching to follow the plot, even though you're no longer enjoying the experience as much.)
So to go back to my earlier comment about a problem with webcomics, you can still only milk a good idea for so long before you need to come up with a new idea. And that's why it's a good thing for shows to end sometimes, instead of getting renewed forever. (It's better when the endings can be planned a bit in advance, though, as opposed to summary cancellation.)
But we still have something new and good. We now have an alternative form of storytelling that didn't really exist before. We can tell longer-form stories that can focus on more subtle character development and more intricate plots. And it's all thanks to the Internet and DVDs.
(P.S.: Yes, I realize I've left out any discussion of soap operas, Asian dramas, telenovelas, comic books, and graphic novels. I'm making no claims that this post is a Complete Theory of Television and Comics. :P)