That's the $64,000 question. As a writing major, I know that many students and professors tend to look down on genre fiction. We university types are preservers of culture, les grandes artistes, blah blah blah, for whom "theme" is a dirty word.
Okay, I'm kidding. Actually we did have a discussion in my fiction writing class this past semester in which we learned (or at least I learned, apparently almost everyone else already knew) that many literary writers apparently really do dislike talking about theme in their writing. And I just don't get that. I could be misunderstanding that attitude, but it seems a lot like you're supposed to "just feel it, man." If an author can't explain, at least in general terms, the message his story or novel is supposed to convey, then I think he's not a very good writer, no matter how technically flawless his writing. I mean, if even you don't know what your story's about, why the heck would I want to read it? Literary does not equal obscure. Literary equals subtle, sensitive, reflective - but never obscure.
The thing is, literary fiction is very difficult to define. That's because oftentimes it can also technically be classed in other genres: historical, ethnic, regional, and yes, even science fiction and fantasy. And so on. I don't think anyone has ever come up with a sufficient definition for literary fiction. The best I can come up with is that the primary concern of literary fiction is internal, rather than external, conflict. Man vs. himself. That doesn't mean there can't be plenty of external conflict in a work of literary fiction. Gone with the Wind has plenty of external conflict of various kinds, but it's still literary. And certain genre works, such as mysteries or romance novels, have their fair share of subtlety and internal conflict.
Sometimes I wonder where all this leaves me. Most of my fiction takes place in an historical setting, and there might even be a good amount of external conflict. But my purpose is mainly the internal struggle of the characters, man vs. himself rather than man vs. man. My professor told me that my work isn't historical fiction but rather literary fiction in an historical setting. So I'll just go with that definition to avoid giving myself a headache.