Like I mentioned in the last entry, I often find myself having to choose a theme, or at least a thematic idea of sorts, to direct my choices for a story I'm building from the ground up. The elderly female naturalist studying that alien world will grow differently based on which direction I choose - environmental, feminist, and so on. The conflicts she's confronted with may not be quite the same between one theme and the next, and the audience might be vastly different. (How many average male SF/F fans are concerned about feminist issues? Maybe more than I think, but that wouldn't be too hard.) So in the beginning, theme has a part to play, and functions sort of like a stage for everything else to take place on. But it doesn't end there, because as you write a story, it changes, and the theme you start out with might not be the one you finish with.
In school, we were encouraged to start with characters and plot points, and leave messy problems like theme for the revision stage, after we had analyzed our stories a couple of times and figured out what we were trying to say. But it often seemed to me that other writers already had a set of themes they were interested in, which tended to show up in their stories regardless of what they thought they were writing about. For example, I'm very attached to the idea that what society calls "evil" is the result of being human, a manifestation of our least-admirable traits and desires, not a nebulous, spiritual source of evil. When I look at my most developed original stories, I see this coming up in every one of them. Characters like Krelian, Lehran, or Maglor probably appeal to me so much because of this personal theme, so it shows up in my reading preferences too. While I rarely start with this theme in mind, it's safe to assume it'll pop up in a certain percentage of them and dictate choices I make, and thus be there for me to polish up later.
My original beef with the statement that Miyazaki wrote theme-driven stories was rooted in this: stories often suggest themes (which is why you can find so many to argue when you're writing for a lit class), and part of the process of refining your work is choosing that theme and playing it up in all aspects of the work (character, plot, setting, dialogue) so it seems that single idea drives everything. He may or may not have started out with a theme in his pocket, but he definitely ended with one, so it directed the content of the final product. Maybe it's a sign of more skill than I possess that he can choose a theme from the beginning, write his story, and play the same theme up in the final draft, but if he did that, if his theme directed all of his character choices, all of his setting and dialogue decisions - does that make it any less a character-driven story? Because when I watched Spirited Away, I did not see a theme-driven story; I saw Chihiro's story. Because the theme was so pervasive, it became more than a motor to drive the story. Rather, it was the frame of the car, which contained all the other parts and mechanisms, while Chihiro was at the wheel. (Yikes.)
I said in a comment to someone that I believe Miyazaki is awesome enough to start with a theme and sneeze out an entire story, complete with characters and what they say and do, all in the space of an hour - but if he can do that, it's experience that makes it possible. Starting with theme does often produce stories that are boring as hell when you read them at the workshop level, but I also doubt the stories I read in college workshops were anywhere close to being finished. Who's to say the boring-ass, theme-driven story you just read for class won't turn into a character-driven, seriously theme-y piece in two more drafts? Nothing.
This is probably very different from what I would've said two years ago. I should go back and look.
Anyway, a theme has no story or personality, and is therefore useless by itself. Without other elements in play (say, a character already made), it can't suggest a story to you, and the characters you might create based on a theme like "there's no such thing as evil, only humanity" are probably not immediately compelling. This is why, when I started thinking about it seriously - and that wasn't too long ago, so my views will probably change a lot as I go - I saw theme as a frame or a stage, something that influences the production (you don't want to walk off into the wings when you're still saying your lines), and not something that might drive a story to the exclusion of the other elements.
Maybe that sounds like an easy answer. The rote, proper answer, straight out of the writing program, is that you can't have a successful story without any of these things, but there are writers out there proving that wrong all over the place. If you're good enough, you can make a story happen without all the other baggage, I'm sure, and make people grateful for it, too. But that harkens back to another thing they love to say in class: you have to master the rules before you break them.
I can see how that might be a problem. It is for me! All the time.
As for theme, and whether it can drive a story by itself, maybe it's just how you think about it. That'll never happen in my conception of story elements as it is right now, because I just don't view it that way. And if I'm completely honest, I almost never consider theme at all - but it keeps showing up, even when I don't want it there.